perldelta: Oust the XS-specific core enhancements

[perl5.git] / pod / perldelta.pod

=encoding utf8

=head1 NAME

perldelta - what is new for perl v5.14.0

=head1 DESCRIPTION

This document describes differences between the 5.12.0 release and
the 5.14.0 release.

Some of the bug fixes in this release have been backported to subsequent
releases of 5.12.x. Those are indicated with the 5.12.x version in
parentheses.

XXX Go through the perl512*delta files and do that.

=head1 Notice

XXX Any important notices here

=head1 Core Enhancements

=head2 Assignment to C<$0> sets the legacy process name with C<prctl()> on Linux

On Linux the legacy process name will be set with L<prctl(2)>, in
addition to altering the POSIX name via C<argv[0]> as perl has done
since version 4.000. Now system utilities that read the legacy process
name such as ps, top and killall will recognize the name you set when
assigning to C<$0>. The string you supply will be cut off at 16 bytes,
this is a limitation imposed by Linux.

=head2 Exception Handling Reliability

Several changes have been made to the way C<die>, C<warn>, and C<$@>
behave, in order to make them more reliable and consistent.

When an exception is thrown inside an C<eval>, the exception is no
longer at risk of being clobbered by code running during unwinding
(e.g., destructors).  Previously, the exception was written into C<$@>
early in the throwing process, and would be overwritten if C<eval> was
used internally in the destructor for an object that had to be freed
while exiting from the outer C<eval>.  Now the exception is written
into C<$@> last thing before exiting the outer C<eval>, so the code
running immediately thereafter can rely on the value in C<$@> correctly
corresponding to that C<eval>.  (C<$@> is still also set before exiting the
C<eval>, for the sake of destructors that rely on this.)

Likewise, a C<local $@> inside an C<eval> will no longer clobber any
exception thrown in its scope.  Previously, the restoration of C<$@> upon
unwinding would overwrite any exception being thrown.  Now the exception
gets to the C<eval> anyway.  So C<local $@> is safe before a C<die>.

Exceptions thrown from object destructors no longer modify the C<$@>
of the surrounding context.  (If the surrounding context was exception
unwinding, this used to be another way to clobber the exception being
thrown.)  Previously such an exception was
sometimes emitted as a warning, and then either was
string-appended to the surrounding C<$@> or completely replaced the
surrounding C<$@>, depending on whether that exception and the surrounding
C<$@> were strings or objects.  Now, an exception in this situation is
always emitted as a warning, leaving the surrounding C<$@> untouched.
In addition to object destructors, this also affects any function call
performed by XS code using the C<G_KEEPERR> flag.

Warnings for C<warn> can now be objects, in the same way as exceptions
for C<die>.  If an object-based warning gets the default handling,
of writing to standard error, it is stringified as
before, with the file and line number appended.  But
a C<$SIG{__WARN__}> handler will now receive an
object-based warning as an object, where previously it was passed the
result of stringifying the object.

=head2 Non-destructive substitution

The substitution (C<s///>) and transliteration
(C<y///>) operators now support an C</r> option that
copies the input variable, carries out the substitution on
the copy and returns the result.  The original remains unmodified.

  my $old = 'cat';
  my $new = $old =~ s/cat/dog/r;
  # $old is 'cat' and $new is 'dog'

This is particularly useful with C<map>.  See L<perlop> for more examples.

=head2 package block syntax

A package declaration can now contain a code block, in which case the
declaration is in scope only inside that block.  So C<package Foo { ... }>
is precisely equivalent to C<{ package Foo; ... }>.  It also works with
a version number in the declaration, as in C<package Foo 1.2 { ... }>.
See L<perlfunc> (434da3..36f77d, 702646).

=head2 perl -h no longer recommends -w

perl -h used to mark the -w option as recommended; since this option is
far less useful than it used to be due to lexical 'use warnings' and since
perl -h is primary a list and brief explanation of the command line switches,
the recommendation has now been removed (60eaec).

=head2 \o{...} for octals

There is a new escape sequence, C<"\o">, in double-quote-like contexts.
It must be followed by braces enclosing an octal number of at least one
digit.  It interpolates as the character with an ordinal value equal to
the octal number.  This construct allows large octal ordinals beyond the
current max of 0777 to be represented.  It also allows you to specify a
character in octal which can safely be concatenated with other regex
snippets and which won't be confused with being a backreference to
a regex capture group.  See L<perlre/Capture groups>.

=head2 C<\N{I<name>}> and C<charnames> enhancements

C<\N{}> and C<charnames::vianame> now know about the abbreviated
character names listed by Unicode, such as NBSP, SHY, LRO, ZWJ, etc., as
well as all the customary abbreviations for the C0 and C1 control
characters (such as ACK, BEL, CAN, etc.), as well as a few new variants
in common usage of some C1 full names.

Unicode has a number of named character sequences, in which particular sequences
of code points are given names.  C<\N{...}> now recognizes these.

C<\N{}>, C<charnames::vianame>, C<charnames::viacode> now know about every
character in Unicode.  Previously, they didn't know about the Hangul syllables
nor a number of CJK (Chinese/Japanese/Korean) characters.

In the past, it was ineffective to override one of Perl's abbreviations
with your own custom alias.  Now it works.

You can also create a custom alias directly to the ordinal of a
character, known by C<\N{...}>, C<charnames::vianame()>, and
C<charnames::viacode()>.  Previously, an alias had to be to an official
Unicode character name.  This made it impossible to create an alias for
a code point that had no name, such as the ones reserved for private
use.  So this change allows you to make more effective use of private
use characters.  Only if there is no official name will
C<charnames::viacode()> return your custom one.

A new function, C<charnames::string_vianame()>, has been added.
This function is a run-time version of C<\N{...}>, returning the string
of characters whose Unicode name is its parameter.  It can handle
Unicode named character sequences, whereas the pre-existing
C<charnames::vianame()> cannot, as the latter returns a single code
point.

See L<charnames> for details on all these changes.

=head2 Uppercase X/B allowed in hexadecimal/binary literals

Literals may now use either upper case C<0X...> or C<0B...> prefixes,
in addition to the already supported C<0x...> and C<0b...>
syntax. (RT#76296) (a674e8d, 333f87f)

C, Ruby, Python and PHP already supported this syntax, and it makes
Perl more internally consistent. A round-trip with C<eval sprintf
"%#X", 0x10> now returns C<16> in addition to C<eval sprintf "%#x",
0x10>, which worked before.

=head2 C<srand()> now returns the seed

This allows programs that need to have repeatable results to not have to come
up with their own seed generating mechanism.  Instead, they can use C<srand()>
and somehow stash the return for future use.  Typical is a test program which
has too many combinations to test comprehensively in the time available to it
each run.  It can test a random subset each time, and should there be a failure,
log the seed used for that run so that it can later be used to reproduce the
exact results.

=head2  C<(?^...)> regex construct added to signify default modifiers

A caret (also called a "circumflex accent") C<"^"> immediately following
a C<"(?"> in a regular expression now means that the subexpression is to
not inherit the surrounding modifiers such as C</i>, but to revert to the
Perl defaults.  Any modifiers following the caret override the defaults.

The stringification of regular expressions now uses this
notation.  E.g., before, C<qr/hlagh/i> would be stringified as
C<(?i-xsm:hlagh)>, but now it's stringified as C<(?^i:hlagh)>.

The main purpose of this is to allow tests that rely on the
stringification to not have to change when new modifiers are added.
See L<perlre/Extended Patterns>.

=head2 C</d>, C</l>, C</u>, C</a>, and C</aa> regular expression modifiers

Four new regular expression modifiers have been added. These are mutually
exclusive; one only can be turned on at a time.

The C</l> modifier says to compile the regular expression as if it were
in the scope of C<use locale>, even if it is not.

The C</u> modifier says to compile the regular expression as if it were
in the scope of a C<use feature "unicode_strings"> pragma.

The C</d> modifier is used to override any C<use locale> and
C<use feature "unicode_strings"> pragmas that are in effect at the time
of compiling the regular expression.

The C</a> regular expression modifier restricts C<\s>, C<\d> and C<\w> and
the Posix (C<[[:posix:]]>) character classes to the ASCII range.  The
complements and C<\b> and C<\B> are correspondingly
affected.  Otherwise, C</a> behaves like the C</u> modifier, in that
case-insensitive matching uses Unicode semantics; for example, "k" will
match the Unicode C<\N{KELVIN SIGN}> under C</i> matching, and code
points in the Latin1 range, above ASCII will have Unicode semantics when
it comes to case-insensitive matching.

The C</aa> modifier is like C</a>, except that, in case-insensitive matching, no ASCII character will match a
non-ASCII character.  For example,

    'k' =~ /\N{KELVIN SIGN}/ai

will match; it won't under C</aa>.

See L<perlre/Modifiers> for more detail.

=head2 Reentrant regular expression engine

It is now safe to use regular expressions within C<(?{...})> and
C<(??{...})> code blocks inside regular expressions.

These block are still experimental, however, and still have problems with
lexical (C<my>) variables, lexical pragmata and abnormal exiting.

=head2 Return value of C<delete $+{...}>

Custom regular expression engines can now determine the return value of
C<delete> on an entry of C<%+> or C<%->.

=head2 Single term prototype

The C<+> prototype is a special alternative to C<$> that will act like
C<\[@%]> when given a literal array or hash variable, but will otherwise
force scalar context on the argument.  This is useful for functions which
should accept either a literal array or an array reference as the argument:

    sub smartpush (+@) {
        my $aref = shift;
        die "Not an array or arrayref" unless ref $aref eq 'ARRAY';
        push @$aref, @_;
    }

When using the C<+> prototype, your function must check that the argument
is of an acceptable type.

=head2 C<use re '/flags';>

The C<re> pragma now has the ability to turn on regular expression flags
till the end of the lexical scope:

    use re '/x';
    "foo" =~ / (.+) /;  # /x implied

See L<re/"'/flags' mode"> for details.

=head2 Statement labels can appear in more places

Statement labels can now occur before any type of statement or declaration,
such as C<package>.

=head2 Array and hash container functions accept references

All built-in functions that operate directly on array or hash
containers now also accept hard references to arrays or hashes:

  |----------------------------+---------------------------|
  | Traditional syntax         | Terse syntax              |
  |----------------------------+---------------------------|
  | push @$arrayref, @stuff    | push $arrayref, @stuff    |
  | unshift @$arrayref, @stuff | unshift $arrayref, @stuff |
  | pop @$arrayref             | pop $arrayref             |
  | shift @$arrayref           | shift $arrayref           |
  | splice @$arrayref, 0, 2    | splice $arrayref, 0, 2    |
  | keys %$hashref             | keys $hashref             |
  | keys @$arrayref            | keys $arrayref            |
  | values %$hashref           | values $hashref           |
  | values @$arrayref          | values $arrayref          |
  | ($k,$v) = each %$hashref   | ($k,$v) = each $hashref   |
  | ($k,$v) = each @$arrayref  | ($k,$v) = each $arrayref  |
  |----------------------------+---------------------------|

This allows these built-in functions to act on long dereferencing chains
or on the return value of subroutines without needing to wrap them in
C<@{}> or C<%{}>:

  push @{$obj->tags}, $new_tag;  # old way
  push $obj->tags,    $new_tag;  # new way

  for ( keys %{$hoh->{genres}{artists}} ) {...} # old way 
  for ( keys $hoh->{genres}{artists}    ) {...} # new way 

For C<push>, C<unshift> and C<splice>, the reference will auto-vivify
if it is not defined, just as if it were wrapped with C<@{}>.

Calling C<keys> or C<values> directly on a reference gives a substantial
performance improvement over explicit dereferencing.

For C<keys>, C<values>, C<each>, when overloaded dereferencing is
present, the overloaded dereference is used instead of dereferencing the
underlying reftype.  Warnings are issued about assumptions made in the
following three ambiguous cases:

  (a) If both %{} and @{} overloading exists, %{} is used
  (b) If %{} overloading exists on a blessed arrayref, %{} is used
  (c) If @{} overloading exists on a blessed hashref, @{} is used

=head2 New global variable C<${^GLOBAL_PHASE}>

A new global variable, C<${^GLOBAL_PHASE}>, has been added to allow
introspection of the current phase of the perl interpreter. It's explained in
detail in L<perlvar/"${^GLOBAL_PHASE}"> and
L<perlmod/"BEGIN, UNITCHECK, CHECK, INIT and END">.

=head2 Unicode Version 6.0 is now supported (mostly)

Perl comes with the Unicode 6.0 data base updated with
L<Corrigendum #8|http://www.unicode.org/versions/corrigendum8.html>,
with one exception noted below.
See L<http://unicode.org/versions/Unicode6.0.0> for details on the new
release.  Perl does not support any Unicode provisional properties,
including the new ones for this release, but their database files are
packaged with Perl.

Unicode 6.0 has chosen to use the name C<BELL> for the character at U+1F514,
which is a symbol that looks like a bell, and used in Japanese cell
phones.  This conflicts with the long-standing Perl usage of having
C<BELL> mean the ASCII C<BEL> character, U+0007.  In Perl 5.14,
C<\N{BELL}> will continue to mean U+0007, but its use will generate a
deprecated warning message, unless such warnings are turned off.  The
new name for U+0007 in Perl will be C<ALERT>, which corresponds nicely
with the existing shorthand sequence for it, C<"\a">.  C<\N{BEL}> will
mean U+0007, with no warning given.  The character at U+1F514 will not
have a name in 5.14, but can be referred to by C<\N{U+1F514}>.  The plan
is that in Perl 5.16, C<\N{BELL}> will refer to U+1F514, and so all code
that uses C<\N{BELL}> should convert by then to using C<\N{ALERT}>,
C<\N{BEL}>, or C<"\a"> instead.

=head2 C<-d:-foo> calls C<Devel::foo::unimport>

The syntax C<-dI<B<:>foo>> was extended in 5.6.1 to make C<-dI<:fooB<=bar>>>
equivalent to C<-MDevel::foo=bar>, which expands
internally to C<use Devel::foo 'bar';>.
F<perl> now allows prefixing the module name with C<->, with the same
semantics as C<-M>, I<i.e.>

=over 4

=item C<-d:-foo>

Equivalent to C<-M-Devel::foo>, expands to
C<no Devel::foo;>, calls C<< Devel::foo->unimport() >>
if the method exists.

=item C<-d:-foo=bar>

Equivalent to C<-M-Devel::foo=bar>, expands to C<no Devel::foo 'bar';>,
calls C<< Devel::foo->unimport('bar') >> if the method exists.

=back

This is particularly useful to suppresses the default actions of a
C<Devel::*> module's C<import> method whilst still loading it for debugging.

=head2 Filehandle method calls load L<IO::File> on demand

When a method call on a filehandle would die because the method cannot
be resolved, and L<IO::File> has not been loaded, Perl now loads L<IO::File>
via C<require> and attempts method resolution again:

  open my $fh, ">", $file;
  $fh->binmode(":raw");     # loads IO::File and succeeds

This also works for globs like STDOUT, STDERR and STDIN:

  STDOUT->autoflush(1);

Because this on-demand load only happens if method resolution fails, the
legacy approach of manually loading an L<IO::File> parent class for partial
method support still works as expected:

  use IO::Handle;
  open my $fh, ">", $file;
  $fh->autoflush(1);        # IO::File not loaded

=head2 Full functionality for C<use feature 'unicode_strings'>

This release provides full functionality for C<use feature
'unicode_strings'>.  Under its scope, all string operations executed and
regular expressions compiled (even if executed outside its scope) have
Unicode semantics.  See L<feature>.

This feature avoids most forms of the "Unicode Bug" (See
L<perlunicode/The "Unicode Bug"> for details.)  If there is a
possibility that your code will process Unicode strings, you are
B<strongly> encouraged to use this subpragma to avoid nasty surprises.

=head2 printf-like functions understand post-1980 size modifiers

Perl's printf and sprintf operators, and Perl's internal printf replacement
function, now understand the C90 size modifiers "hh" (C<char>), "z"
(C<size_t>), and "t" (C<ptrdiff_t>).  Also, when compiled with a C99
compiler, Perl now understands the size modifier "j" (C<intmax_t>).

So, for example, on any modern machine, C<sprintf('%hhd', 257)> returns '1'.

=head2 DTrace probes now include package name

The DTrace probes now include an additional argument (C<arg3>) which contains
the package the subroutine being entered or left was compiled in.

For example using the following DTrace script:

  perl$target:::sub-entry
  {
      printf("%s::%s\n", copyinstr(arg0), copyinstr(arg3));
  }

and then running:

  perl -e'sub test { }; test'

DTrace will print:

  main::test

=head2 Stacked labels

Multiple statement labels can now appear before a single statement.

=head2 Any unsigned value can be encoded as a character

With this release, Perl is adopting a model that any unsigned value can
be treated as a code point and encoded internally (as utf8) without
warnings -- not just the code points that are legal in Unicode.
However, unless utf8 warnings have been
explicitly lexically turned off, outputting or performing a
Unicode-defined operation (such as upper-casing) on such a code point
will generate a warning.  Attempting to input these using strict rules
(such as with the C<:encoding('UTF-8')> layer) will continue to fail.
Prior to this release the handling was very inconsistent, and incorrect
in places.  Also, the Unicode non-characters, some of which previously were
erroneously considered illegal in places by Perl, contrary to the Unicode
standard, are now always legal internally.  But inputting or outputting
them will work the same as for the non-legal Unicode code points, as the
Unicode standard says they are illegal for "open interchange".

=head2 Regular expression debugging output improvement

Regular expression debugging output (turned on by C<use re 'debug';>) now
uses hexadecimal when escaping non-ASCII characters, instead of octal.

=head2 Add C<\p{Titlecase}> as a synonym for C<\p{Title}>

This synonym is added for symmetry with the Unicode property names
C<\p{Uppercase}> and C<\p{Lowercase}>.

=head2 New warnings categories for problematic (non-)Unicode code points.

Three new warnings subcategories of <utf8> have been added.  These
allow you to turn off warnings for their covered events, while allowing
the other UTF-8 warnings to remain on.  The three categories are:
C<surrogate> when UTF-16 surrogates are encountered;
C<nonchar> when Unicode non-character code points are encountered;
and C<non_unicode> when code points that are above the legal Unicode
maximum of 0x10FFFF are encountered.

=head1 Security

=head2 Restrict \p{IsUserDefined} to In\w+ and Is\w+

In L<perlunicode/"User-Defined Character Properties">, it says you can
create custom properties by defining subroutines whose names begin with
"In" or "Is". However, perl doesn't actually enforce that naming
restriction, so \p{foo::bar} will call foo::Bar() if it exists.

This commit finally enforces this convention. Note that this broke a
number of existing tests for properties, since they didn't always use an
Is/In prefix.

=head2 User-defined regular expression properties

Perl no longer allows a tainted regular expression to invoke a user-defined
property via C<\p{...}> syntax. It simply dies instead [perl #82616].

=head1 Incompatible Changes

=head2 "C<\cI<X>>"

The backslash-c construct was designed as a way of specifying
non-printable characters, but there were no restrictions (on ASCII
platforms) on what the character following the C<c> could be.  Now, that
character must be one of the ASCII characters.

=head2 localised tied hashes, arrays and scalars are no longed tied

In the following:

    tie @a, ...;
    {
	local @a;
	# here, @a is a now a new, untied array
    }
    # here, @a refers again to the old, tied array

The new local array used to be made tied too, which was fairly pointless,
and has now been fixed. This fix could however potentially cause a change
in behaviour of some code.

=head2 C<given> return values

Starting from this release, C<given> blocks returns the last evaluated
expression, or an empty list if the block was exited by C<break>. Thus you
can now write:

    my $type = do {
     given ($num) {
      break     when undef;
      'integer' when /^[+-]?[0-9]+$/;
      'float'   when /^[+-]?[0-9]+(?:\.[0-9]+)?$/;
      'unknown';
     }
    };

See L<perlsyn/Return value> for details.

=head2 localised tied scalars are tied again.

The change in behaviour in 5.13.1 of localising tied scalar values has
been reverted to the existing 5.12.0 and earlier behaviour (the change for
arrays and hashes remains).

=head2 Naming fixes in Policy_sh.SH may invalidate Policy.sh

Several long-standing typos and naming confusions in Policy_sh.SH have
been fixed, standardizing on the variable names used in config.sh.

This will change the behavior of Policy.sh if you happen to have been
accidentally relying on the Policy.sh incorrect behavior. We'd appreciate
feedback from anyone using Policy.sh to be sure nothing is broken by
this change (c1bd23).

=head2 Stashes are now always defined

C<defined %Foo::> now always returns true, even when no symbols have yet been
defined in that package.

This is a side effect of removing a special case kludge in the tokeniser,
added for 5.10.0, to hide side effects of changes to the internal storage of
hashes that to drastically reduce their memory usage overhead.

Calling defined on a stash has been deprecated since 5.6.0, warned on
lexicals since 5.6.0, and has warned for stashes (and other package
variables) since 5.12.0. C<defined %hash> has always exposed an
implementation detail - emptying a hash by deleting all entries from it does
not make C<defined %hash> false, hence C<defined %hash> is not valid code to
determine whether an arbitrary hash is empty. Instead, use the behaviour
that an empty C<%hash> always returns false in a scalar context.

=head2 \400 - \777

Use of C<\400> - C<\777> in regexes in certain circumstances has given
different, anomalous behavior than their use in all other
double-quote-like contexts.   Since 5.10.1, a deprecated warning message
has been raised when this happens.  Now, all double-quote-like contexts
have the same behavior, namely to be equivalent to C<\x{100}> -
C<\x{1FF}>, with no deprecation warning. Use of these values in the
command line option C<"-0"> retains the current meaning to slurp input
files whole; previously, this was documented only for C<"-0777">.  It is
recommended, however, because of various ambiguities, to use the new
C<\o{...}> construct to represent characters in octal.
(fa1639c..f6993e9).

=head2 Declare API incompatibility between blead releases

Only stable releases (5.10.x, 5.12.x, 5.14.x, ...) guarantee binary
compatibility with each other, while blead releases (5.13.x, 5.15.x, ...) often
break this compatibility. However, prior to perl 5.13.4, all blead releases had
the same C<PERL_API_REVISION>, C<PERL_API_VERSION>, and C<PERL_API_SUBVERSION>,
effectively declaring them as binary compatible, which they weren't. From now
on, blead releases will have a C<PERL_API_SUBVERSION> equal to their
C<PERL_SUBVERSION>, explicitly marking them as incompatible with each other.

Maintenance releases of stable perl versions will continue to make no
intentionally incompatible API changes.

=head2 Check API compatibility when loading XS modules

When perl's API changes in incompatible ways (which usually happens between
every major release), XS modules compiled for previous versions of perl will not
work anymore. They will need to be recompiled against the new perl.

In order to ensure that modules are recompiled, and to prevent users from
accidentally loading modules compiled for old perls into newer ones, the
C<XS_APIVERSION_BOOTCHECK> macro has been added. That macro, which is called
when loading every newly compiled extension, compares the API version of the
running perl with the version a module has been compiled for and raises an
exception if they don't match.

=head2 Binary Incompatible with all previous Perls

Some bit fields have been reordered; therefore, this release will not be binary
compatible with any previous Perl release.

=head2 Change in the parsing of certain prototypes

Functions declared with the following prototypes now behave correctly as unary
functions:

=over 4

=item *

C<*>

=item *

C<\sigil>

=item *

C<\[...]>

=item *

C<;$>

=item *

C<;*>

=item *

C<;\sigil>

=item *

C<;\[...]>

=back

Due to this bug fix, functions using the C<(*)>, C<(;$)> and C<(;*)> prototypes
are parsed with higher precedence than before. So in the following example:

  sub foo($);
  foo $a < $b;

the second line is now parsed correctly as C<< foo($a) < $b >>, rather than
C<< foo($a < $b) >>. This happens when one of these operators is used in
an unparenthesised argument:

  < > <= >= lt gt le ge
  == != <=> eq ne cmp ~~
  &
  | ^
  &&
  || //
  .. ...
  ?:
  = += -= *= etc.

=head2 Magic variables outside the main package

In previous versions of Perl, magic variables like C<$!>, C<%SIG>, etc. would
'leak' into other packages.  So C<%foo::SIG> could be used to access signals,
C<${"foo::!"}> (with strict mode off) to access C's C<errno>, etc.

This was a bug, or an 'unintentional' feature, which caused various ill effects,
such as signal handlers being wiped when modules were loaded, etc.

This has been fixed (or the feature has been removed, depending on how you see
it).

=head2 Smart-matching against array slices

Previously, the following code resulted in a successful match:

    my @a = qw(a y0 z);
    my @b = qw(a x0 z);
    @a[0 .. $#b] ~~ @b;

This odd behaviour has now been fixed [perl #77468].

=head2 C API changes

The first argument of the C API function C<Perl_fetch_cop_label> has changed
from C<struct refcounted he *> to C<COP *>, to better insulate the user from
implementation details.

This API function was marked as "may change", and likely isn't in use outside
the core.  (Neither an unpacked CPAN, nor Google's codesearch, finds any other
references to it.)

=head2 Stringification of regexes has changed

Default regular expression modifiers are now notated by using
C<(?^...)>.  Code relying on the old stringification will fail.  The
purpose of this is so that when new modifiers are added, such code will
not have to change (after this one time), as the stringification will
automatically incorporate the new modifiers.

Code that needs to work properly with both old- and new-style regexes
can avoid the whole issue by using (for Perls since 5.9.5):

 use re qw(regexp_pattern);
 my ($pat, $mods) = regexp_pattern($re_ref);

where C<$re_ref> is a reference to a compiled regular expression.  Upon
return, C<$mods> will be a string containing all the non-default
modifiers used when the regular expression was compiled, and C<$pattern>
the actual pattern.

If the actual stringification is important, or older Perls need to be
supported, you can use something like the following:

    # Accept both old and new-style stringification
    my $modifiers = (qr/foobar/ =~ /\Q(?^/) ? '^' : '-xism';

And then use C<$modifiers> instead of C<-xism>.

=head2 Regular expressions retain their localeness when interpolated

Regular expressions compiled under C<"use locale"> now retain this when
interpolated into a new regular expression compiled outside a
C<"use locale">, and vice-versa.

Previously, a regular expression interpolated into another one inherited
the localeness of the surrounding one, losing whatever state it
originally had.  This is considered a bug fix, but may trip up code that
has come to rely on the incorrect behavior.

=head2 Directory handles not copied to threads

On systems that do not have a C<fchdir> function, newly-created threads no
longer inherit directory handles from their parent threads. Such programs
would probably have crashed anyway [perl #75154].

=head2 Negation treats strings differently from before

The unary negation operator C<-> now treats strings that look like numbers
as numbers [perl #57706].

=head2 Negative zero

Negative zero (-0.0), when converted to a string, now becomes "0" on all
platforms. It used to become "-0" on some, but "0" on others.

If you still need to determine whether a zero is negative, use
C<sprintf("%g", $zero) =~ /^-/> or the L<Data::Float> module on CPAN.

=head2 Dereferencing typeglobs

If you assign a typeglob to a scalar variable:

    $glob = *foo;

the glob that is copied to C<$glob> is marked with a special flag
indicating that the glob is just a copy. This allows subsequent assignments
to C<$glob> to overwrite the glob. The original glob, however, is
immutable.

Many Perl operators did not distinguish between these two types of globs.
This would result in strange behaviour in edge cases: C<untie $scalar>
would do nothing if the last thing assigned to the scalar was a glob
(because it treated it as C<untie *$scalar>, which unties a handle).
Assignment to a glob slot (e.g., C<(*$glob) = \@some_array>) would simply
assign C<\@some_array> to C<$glob>.

To fix this, the C<*{}> operator (including the C<*foo> and C<*$foo> forms)
has been modified to make a new immutable glob if its operand is a glob
copy. Various operators that make a distinction between globs and scalars
have been modified to treat only immutable globs as globs.

This causes an incompatible change in code that assigns a glob to the
return value of C<*{}> when that operator was passed a glob copy. Take the
following code, for instance:

    $glob = *foo;
    *$glob = *bar;

The C<*$glob> on the second line returns a new immutable glob. That new
glob is made an alias to C<*bar>. Then it is discarded. So the second
assignment has no effect.

It also means that C<tie $handle> will now tie C<$handle> as a scalar, even
if it has had a glob assigned to it.

The upside to this incompatible change is that bugs [perl #77496],
[perl #77502], [perl #77508], [perl #77688], and [perl #77812],
and maybe others, too, have been fixed.

See L<http://rt.perl.org/rt3/Public/Bug/Display.html?id=77810> for even
more detail.

=head2 Clearing stashes

Stash list assignment C<%foo:: = ()> used to make the stash anonymous
temporarily while it was being emptied. Consequently, any of its
subroutines referenced elsewhere would become anonymous (showing up as
"(unknown)" in C<caller>). Now they retain their package names, such that
C<caller> will return the original sub name if there is still a reference
to its typeglob, or "foo::__ANON__" otherwise [perl #79208].

=head2 C<:=> is now a syntax error

Previously C<my $pi := 4;> was exactly equivalent to C<my $pi : = 4;>,
with the C<:> being treated as the start of an attribute list, ending before
the C<=>. The use of C<:=> to mean C<: => was deprecated in 5.12.0, and is now
a syntax error. This will allow the future use of C<:=> as a new token.

We find no Perl 5 code on CPAN using this construction, outside the core's
tests for it, so we believe that this change will have very little impact on
real-world codebases.

If it is absolutely necessary to have empty attribute lists (for example,
because of a code generator) then avoid the error by adding a space before
the C<=>.

=head2 Run-time code block in regular expressions

Code blocks in regular expressions (C<(?{...})> and C<(??{...})>) used not
to inherit any pragmata (strict, warnings, etc.) if the regular expression
was compiled at run time as happens in cases like these two:

  use re 'eval';
  $foo =~ $bar; # when $bar contains (?{...})
  $foo =~ /$bar(?{ $finished = 1 })/;

This was a bug, which has now been fixed. But it has the potential to break
any code that was relying on this bug.

=head2 All objects are destroyed

It used to be possible to prevent a destructor from being called during
global destruction by artificially increasing the reference count of an
object.

Now such objects I<will> will be destroyed, as a result of a bug fix
[perl #81230].

This has the potential to break some XS modules. (In fact, it break some.
See L</Known Problems>, below.)

=head2 Most C<\p{}> properties are now immune from case-insensitive matching

For most Unicode properties, it doesn't make sense to have them match
differently under C</i> case-insensitive matching than not.  And doing
so leads to unexpected results and potential security holes.  For
example

 m/\p{ASCII_Hex_Digit}+/i

could previously match non-ASCII characters because of the Unicode
matching rules.  There were a number of bugs in this feature until an
earlier release in the 5.13 series.  Now this release reverts, and
removes the feature completely except for the few properties where
people have come to expect it, namely the ones where casing is an
integral part of their functionality, such as C<m/\p{Uppercase}/i> and
C<m/\p{Lowercase}/i>, both of which match the exact same code points,
namely those matched by C<m/\p{Cased}/i>.  Details are in
L<perlrecharclass/Unicode Properties>.

User-defined property handlers that need to match differently under
C</i> must change to read the new boolean parameter passed it which is
non-zero if case-insensitive matching is in effect; 0 if not.  See
L<perluniprops/User-Defined Character Properties>.

=head2 regex: \p{} in pattern implies Unicode semantics

Now, a Unicode property match specified in the pattern will indicate
that the pattern is meant for matching according to Unicode rules
(e40e74f)

=head2 add GvCV_set() and GvGP_set() macros and change GvGP()

This allows a future commit to eliminate some backref magic between GV
and CVs, which will require complete control over assignment to the
gp_cv slot.

If you've been using GvGP() in lvalue context this change will break
your code, you should use GvGP_set() instead. (c43ae56)

=head2 _swash_inversion_hash is no longer exported as part of the API

This function shouldn't be called from XS code. (4c2e113)

=head2 Unreferenced objects in global destruction

The fix for [perl #36347], which made sure that destructors were called on
unreferenced objects, broke the tests for three CPAN modules, which
apparently rely on the bug.

To provide more time for fixing them (as this is such a minor bug), we
have reverted the fix until after perl 5.14.0.

This resolves [perl #82542] and other related tickets.

=head2 C<close> on shared pipes

The C<close> function no longer waits for the child process to exit if the
underlying file descriptor is still in use by another thread, to avoid
deadlocks. It returns true in such cases.

=head2 Passing references to warn()

An earlier Perl 5.13.x release changed C<warn($ref)> to leave the reference
unchanged, allowing C<$SIG{__WARN__}> handlers to access the original
reference. But this stopped warnings that were references from having the
file and line number appended even when there was no C<$SIG{__WARN__}>
handler in place.

Now C<warn> checks for the presence of such a handler and, if there is
none, proceeds to stringify the reference and append the file and line
number. This allows simple uses of C<warn> for debugging to continue to
work as they did before.

=head1 Deprecations

The following items are now deprecated.

=over 4

=item C<Perl_ptr_table_clear>

C<Perl_ptr_table_clear> is no longer part of Perl's public API. Calling it now
generates a deprecation warning, and it will be removed in a future
release.

=item *

Omitting a space between a regex pattern or pattern modifiers and the following
word is deprecated.  For example, C<< m/foo/sand $bar >> will still be parsed
as C<< m/foo/s and $bar >> but will issue a warning.

=back

=head2 Omitting a space between a regular expression and subsequent word

Omitting a space between a regex pattern or pattern modifiers and the
following word is deprecated. Deprecation for regular expression
I<matches> was added in Perl 5.13.2.  In this release, the deprecation
is extended to regular expression I<substitutions>. For example,
C<< s/foo/bar/sand $bar >> will still be parsed as
C<< s/foo/bar/s and $bar >> but will issue a warning. (aa78b66)

=head2 Deprecation warning added for deprecated-in-core .pl libs

This is a mandatory warning, not obeying -X or lexical warning bits.
The warning is modelled on that supplied by deprecate.pm for
deprecated-in-core .pm libraries.  It points to the specific CPAN
distribution that contains the .pl libraries. The CPAN version, of
course, does not generate the warning. (0111154)

=head2 List assignment to C<$[>

After assignment to C<$[> has been deprecated and started to give warnings in
perl version 5.12.0, this version of perl also starts to emit a warning when
assigning to C<$[> in list context. This fixes an oversight in 5.12.0.

=head2 Use of qw(...) as parentheses

Historically the parser fooled itself into thinking that C<qw(...)> literals
were always enclosed in parentheses, and as a result you could sometimes omit
parentheses around them:

    for $x qw(a b c) { ... }

The parser no longer lies to itself in this way.  Wrap the list literal in
parentheses, like:

    for $x (qw(a b c)) { ... }

=head2 C<\N{BELL}> is deprecated

This is because Unicode is using that name for a different character.
See L</Unicode Version 6.0 is now supported (mostly)> for more
explanation.

=head2 C<?PATTERN?> is deprecated

C<?PATTERN?> (without the initial m) has been deprecated and now produces
a warning.  This is to allow future use of C<?> in new operators.
The match-once functionality is still available in the form of C<m?PATTERN?>.

=head2 C<sv_compile_2op()> is now deprecated

The C<sv_compile_2op()> API function is now deprecated. Searches suggest
that nothing on CPAN is using it, so this should have zero impact.

It attempted to provide an API to compile code down to an optree, but failed
to bind correctly to lexicals in the enclosing scope. It's not possible to
fix this problem within the constraints of its parameters and return value.

=head2 Tie functions on scalars holding typeglobs

Calling a tie function (C<tie>, C<tied>, C<untie>) with a scalar argument
acts on a file handle if the scalar happens to hold a typeglob.

This is a long-standing bug that will be removed in Perl 5.16, as
there is currently no way to tie the scalar itself when it holds
a typeglob, and no way to untie a scalar that has had a typeglob
assigned to it.

This bug was fixed in 5.13.7 but, because of the breakage it caused, the
fix has been reverted. Now there is a deprecation warning whenever a tie
function is used on a handle without an explicit C<*>.

=over

=item Deprecated Modules

The following modules will be removed from the core distribution in a
future release, and should be installed from CPAN instead. Distributions
on CPAN which require these should add them to their prerequisites. The
core versions of these modules warnings will issue a deprecation warning.

If you ship a packaged version of Perl, either alone or as part of a
larger system, then you should carefully consider the repercussions of
core module deprecations. You may want to consider shipping your default
build of Perl with packages for some or all deprecated modules which
install into C<vendor> or C<site> perl library directories. This will
inhibit the deprecation warnings.

Alternatively, you may want to consider patching F<lib/deprecate.pm>
to provide deprecation warnings specific to your packaging system
or distribution of Perl, consistent with how your packaging system
or distribution manages a staged transition from a release where the
installation of a single package provides the given functionality, to
a later release where the system administrator needs to know to install
multiple packages to get that same functionality.

You can silence these deprecation warnings by installing the modules
in question from CPAN.  To install the latest version of all of them,
just install C<Task::Deprecations::5_14>.

=over

=item L<Devel::DProf>

We strongly recommend that you install and used L<Devel::NYTProf> in
preference, as it offers significantly improved profiling and reporting.

=back

=back

=head2 User-defined case-mapping

This feature is being deprecated due to its many issues, as documented in
L<perlunicode/User-Defined Case Mappings (for serious hackers only)>.
It is planned to remove this feature in Perl 5.16.  A CPAN module
providing improved functionality is being prepared for release by the
time 5.14 is.

=head1 Performance Enhancements

=head2 "safe signals" optimization

Signal dispatch has been moved from the runloop into control ops. This
should give a few percent speed increase, and eliminates almost all of
the speed penalty caused by the introduction of "safe signals" in
5.8.0. Signals should still be dispatched within the same statement as
they were previously - if this is not the case, or it is possible to
create uninterruptible loops, this is a bug, and reports are encouraged
of how to recreate such issues.

=head2 Optimization of shift; and pop; calls without arguments

Additional two OPs are not added anymore into op tree for shift and pop
calls without argument (when it works on C<@_>). Makes C<shift;> 5%
faster over C<shift @_;> on not threaded perl and 25% faster on threaded.

=head2 Adjacent pairs of nextstate opcodes are now optimized away

Previously, in code such as

    use constant DEBUG => 0;

    sub GAK {
        warn if DEBUG;
        print "stuff\n";
    }

the ops for C<warn if DEBUG;> would be folded to a C<null> op (C<ex-const>), but
the C<nextstate> op would remain, resulting in a runtime op dispatch of
C<nextstate>, C<nextstate>, ...

The execution of a sequence of C<nextstate> ops is indistinguishable from just
the last C<nextstate> op so the peephole optimizer now eliminates the first of
a pair of C<nextstate> ops, except where the first carries a label, since labels
must not be eliminated by the optimizer and label usage isn't conclusively known
at compile time.

=head2 blah blah blah

Only allocate entries for @_ on demand - this not only saves memory per
subroutine defined but should hopefully improve COW behaviour (77bac2).

=head2 Multiple small improvements to threads

The internal structures of threading now make fewer API calls and fewer
allocations, resulting in noticeably smaller object code. Additionally,
many thread context checks have been deferred so that they're only done
when required (although this is only possible for non-debugging builds).

=head2 Size optimisations to SV and HV structures

xhv_fill has been eliminated from struct xpvhv, saving 1 IV per hash and
on some systems will cause struct xpvhv to become cache aligned. To avoid
this memory saving causing a slowdown elsewhere, boolean use of HvFILL
now calls HvTOTALKEYS instead (which is equivalent) - so while the fill
data when actually required is now calculated on demand, the cases when
this needs to be done should be few and far between (f4431c .. fcd245).

The order of structure elements in SV bodies has changed. Effectively,
the NV slot has swapped location with STASH and MAGIC. As all access to
SV members is via macros, this should be completely transparent. This
change allows the space saving for PVHVs documented above, and may reduce
the memory allocation needed for PVIVs on some architectures.

=head2 Optimisation of regexp engine string comparison work

The foldEQ_utf8 API function for case-insensitive comparison of strings (which
is used heavily by the regexp engine) was substantially refactored and
optimised - and its documentation much improved as a free bonus gift
(8b3587, e6226b).

=head2 Memory consumption improvements to Exporter

The @EXPORT_FAIL AV is no longer created unless required, hence neither is
the typeglob backing it - this saves about 200 bytes per Exporter using
package that doesn't use this functionality.

=head2 blah blah blah

There are several small optimizations to reduce CPU cache misses in various very
commonly used modules like C<warnings> and C<Carp> as well in accessing
file-handles for reading. (5.13.3)

XXX These need to be changed to =head2 entries, or the entries above need
to change:

=over 4

=item *

Make string appending 100 times faster

When doing a lot of string appending, perl could end up allocating a lot more
memory than needed in a very inefficient way, if perl was configured to use the
system's C<malloc> implementation instead of its own.

C<sv_grow>, which is what's being used to allocate more memory if necessary when
appending to a string, has now been taught how to round up the memory it
requests to a certain geometric progression, making it much faster on certain
platforms and configurations. On Win32, it's now about 100 times faster.

=item *

For weak references, the common case of just a single weak reference per
referent has been optimised to reduce the storage required. In this case it
saves the equivalent of one small perl array per referent.

=item *

C<XPV>, C<XPVIV>, and C<XPVNV> now only allocate the parts of the C<SV> body
they actually use, saving some space.

=item *

Scalars containing regular expressions now only allocate the part of the C<SV>
body they actually use, saving some space.

=item *

Compiling regular expressions has been made faster for the case where upgrading
the regex to utf8 is necessary but that isn't known when the compilation begins.

=item *

The bulk of the C<Tie::Hash::NamedCapture> module used to be in the perl
core. It has now been moved to an XS module, to reduce the overhead for
programs that do not use C<%+> or C<%->.

=item *

Eliminate C<PL_*> accessor functions under ithreads.

When C<MULTIPLICITY> was first developed, and interpreter state moved into an
interpreter struct, thread and interpreter local C<PL_*> variables were defined
as macros that called accessor functions, returning the address of the value,
outside of the perl core. The intent was to allow members within the interpreter
struct to change size without breaking binary compatibility, so that bug fixes
could be merged to a maintenance branch that necessitated such a size change.

However, some non-core code defines C<PERL_CORE>, sometimes intentionally to
bypass this mechanism for speed reasons, sometimes for other reasons but with
the inadvertent side effect of bypassing this mechanism. As some of this code is
widespread in production use, the result is that the core B<can't> change the
size of members of the interpreter struct, as it will break such modules
compiled against a previous release on that maintenance branch. The upshot is
that this mechanism is redundant, and well-behaved code is penalised by
it. Hence it can and should be removed.

=item *

When an object has many weak references to it, freeing that object
can under some some circumstances take O(N^2) time to free (where N is the
number of references). The number of circumstances has been reduced
[perl #75254]

=item *

An earlier optimisation to speed up C<my @array = ...> and
C<my %hash = ...> assignments caused a bug and was disabled in Perl 5.12.0.

Now we have found another way to speed up these assignments [perl #82110].

=back

=head1 Modules and Pragmata

=head2 New Modules and Pragmata

=over 4

=item *

C<CPAN::Meta::YAML> 0.003 has been added as a dual-life module.  It supports a
subset of YAML sufficient for reading and writing META.yml and MYMETA.yml files
included with CPAN distributions or generated by the module installation
toolchain. It should not be used for any other general YAML parsing or
generation task.

=item *

C<CPAN::Meta> version 2.110440 has been added as a dual-life module. It
provides a standard library to read, interpret and write CPAN distribution
metadata files (e.g. META.json and META.yml) which describes a
distribution, its contents, and the requirements for building it and
installing it. The latest CPAN distribution metadata specification is
included as C<CPAN::Meta::Spec> and notes on changes in the specification
over time are given in C<CPAN::Meta::History>.

=item *

C<HTTP::Tiny> 0.010 has been added as a dual-life module.  It is a very
small, simple HTTP/1.1 client designed for simple GET requests and file
mirroring.  It has has been added to enable CPAN.pm and CPANPLUS to
"bootstrap" HTTP access to CPAN using pure Perl without relying on external
binaries like F<curl> or F<wget>.

=item *

C<JSON::PP> 2.27105 has been added as a dual-life module, for the sake of
reading F<META.json> files in CPAN distributions.

=item *

C<Module::Metadata> 1.000003 has been added as a dual-life module.  It gathers
package and POD information from Perl module files.  It is a standalone module
based on Module::Build::ModuleInfo for use by other module installation
toolchain components.  Module::Build::ModuleInfo has been deprecated in
favor of this module instead.

=item *

C<Perl::OSType> 1.002 has been added as a dual-life module.  It maps Perl
operating system names (e.g. 'dragonfly' or 'MSWin32') to more generic types
with standardized names (e.g.  "Unix" or "Windows").  It has been refactored
out of Module::Build and ExtUtils::CBuilder and consolidates such mappings into
a single location for easier maintenance.

=item *

The following modules were added by the C<Unicode::Collate> 
upgrade. See below for details.

C<Unicode::Collate::CJK::Big5>

C<Unicode::Collate::CJK::GB2312>

C<Unicode::Collate::CJK::JISX0208>

C<Unicode::Collate::CJK::Korean>

C<Unicode::Collate::CJK::Pinyin>

C<Unicode::Collate::CJK::Stroke>

=item *

C<Version::Requirements> version 0.101020 has been added as a dual-life
module.  It provides a standard library to model and manipulates module
prerequisites and version constraints as defined in the L<CPAN::Meta::Spec>.

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

XXX Where does this go in the list?

Perl 4 C<.pl> libraries

These historical libraries have been minimally modified to avoid using
C<$[>.  This is to prepare them for the deprecation of C<$[>.

=item *

C<Archive::Extract> has been upgraded from version 0.38 to 0.48.

Updates since 0.38 include: a safe print method that guards
Archive::Extract from changes to $\; a fix to the tests when run in core
perl; support for TZ files; and a modification for the lzma logic to favour
IO::Uncompress::Unlzma

Resolves an issue with NetBSD-current and its new unzip 
executable.

=item *

C<Archive::Tar> has been upgraded from version 1.54 to 1.76.

Important changes since 1.54 include: compatibility with busybox
implementations of tar; a fix so that C<write()> and C<create_archive()>
close only handles they opened; and a bug was fixed regarding the exit code
of extract_archive. (afabe0e)

Among other things, the new version adds a new option to C<ptar> to allow safe
creation of tarballs without world-writable files on Windows, allowing those
archives to be uploaded to CPAN.

This adds the ptargrep utility for using regular expressions against 
the contents of files in a tar archive.

Skip extracting pax extended headers.

=item *

C<autodie> has been upgraded from version 2.06_01 to 2.1001.

=item *

C<B> has been upgraded from version 1.23 to 1.27.

It no longer crashes when taking apart a C<y///> containing characters
outside the octet range or compiled in a C<use utf8> scope.

The size of the shared object has been reduced by about 40%, with no
reduction in functionality.

=item *

C<B::Concise> has been upgraded from version 0.78 to 0.82.

B::Concise marks rv2sv, rv2av and rv2hv ops with the new OPpDEREF flag
as "DREFed".

It no longer produces mangled output with the C<-tree> option
[perl #80632].

=item *

C<B::Debug> has been upgraded from version 1.12 to 1.16.

=item *

C<B::Deparse> has been upgraded from version 0.96 to 1.02.

A bug has been fixed when deparsing a nextstate op that has both a
change of package (relative to the previous nextstate), or a change of
C<%^H> or other state, and a label.  Previously the label was emitted
first, leading to syntactically invalid output because a label is not
permitted immediately before a package declaration, B<BEGIN> block,
or some other things.  Now the label is emitted last.

The 'no 5.13.2' or similar form is now correctly handled by B::Deparse.

B::Deparse now properly handles the code that applies a conditional
pattern match against implicit C<$_> as it was fixed in [perl #20444].

It fixes deparsing of C<our> followed by a variable with funny characters
(as permitted under the C<utf8> pragma) [perl #33752].

=item *

C<B::Lint> has been upgraded from version 1.11_01 to 1.12.

=item *

C<base> has been upgraded from version 2.15 to 2.16.

=item *

C<bignum> has been upgraded from version 0.23 to 0.25.

=item *

C<blib> has been upgraded from version 1.04 to 1.06.

=item *

C<Carp> has been upgraded from version 1.18 to 1.19.

L<Carp> now detects incomplete L<caller()|perlfunc/"caller EXPR"> overrides and
avoids using bogus C<@DB::args>. To provide backtraces, Carp relies on
particular behaviour of the caller built-in. Carp now detects if other code has
overridden this with an incomplete implementation, and modifies its backtrace
accordingly. Previously incomplete overrides would cause incorrect values in
backtraces (best case), or obscure fatal errors (worst case)

This fixes certain cases of C<Bizarre copy of ARRAY> caused by modules
overriding C<caller()> incorrectly.

It now avoids using regular expressions that cause perl to
load its Unicode tables, in order to avoid the 'BEGIN not safe after
errors' error that will ensue if there has been a syntax error
[perl #82854].

=item *

C<CGI> has been upgraded from version 3.48 to 3.51.

This provides the following security fixes: the MIME boundary in 
multipart_init is now random and improvements to the handling of 
newlines embedded in header values.

The documentation for param_fetch() has been corrected and clarified.

=item *

C<charnames> has been upgraded from version 1.07 to 1.10.

C<viacode()> is now significantly faster.

=item *

C<Compress::Raw::Bzip2> has been upgraded from version 2.024 to 2.033.

Updated to use bzip2 1.0.6

=item *

C<Compress::Raw::Zlib> has been upgraded from version 2.024 to 2.033.

=item *

C<Compress::Zlib> has been upgraded from version 2.024 to 2.027.

=item *

C<CPAN> has been upgraded from version 1.94_56 to 1.94_63.

=over 4

=item * release 1.94_57

=item * bugfix: treat modules correctly that are deprecated in perl 5.12.

=item * bugfix: RT #57482 and #57788 revealed that configure_requires
implicitly assumed build_requires instead of normal requires. (Reported
by Andrew Whatson and Father Chrysostomos respectively)

=item * testfix: solaris should run the tests without expect because (some?)
solaris have a broken expect 

=item * testfix: run tests with cache_metadata off to prevent spill over
effects from previous test runs

=back

Includes support for META.json and MYMETA.json.

=item *

C<CPANPLUS> has been upgraded from version 0.90 to 0.9102.

Fixed the shell test to skip if test is not being run under a terminal;
resolved the issue where a prereq on Config would not be recognised as a
core module.

Includes support for META.json and MYMETA.json and a change to
using Digest::SHA for CPAN checksums.

=item *

C<CPANPLUS::Dist::Build> has been upgraded from version 0.46 to 0.54.

=item *

C<Cwd> has been upgraded from version 3.31 to 3.36.

=item *

C<Data::Dumper> has been upgraded from version 2.125 to 2.130_02.

The indentation used to be off when C<$Data::Dumper::Terse> was set. This
has been fixed [perl #73604].

This fixes a crash when using custom sort functions that might cause the stack
to change.

C<Dumpxs> no longer crashes with globs returned by C<*$io_ref>
[perl #72332].

=item *

C<DB_File> has been upgraded from version 1.820 to 1.821.

=item *

C<deprecate> has been upgraded from version 0.01 to 0.02.

=item *

C<Devel::DProf> has been upgraded from version 20080331.00 to 20110228.00.

Merely loading C<Devel::DProf> now no longer triggers profiling to start.
C<use Devel::DProf> and C<perl -d:DProf ...> still behave as before and start
the profiler.

NOTE: C<Devel::DProf> is deprecated and will be removed from a future
version of Perl. We strongly recommend that you install and use
L<Devel::NYTProf> instead, as it offers significantly improved
profiling and reporting.

=item *

C<Devel::Peek> has been upgraded from version 1.04 to 1.06.

=item *

C<Devel::SelfStubber> has been upgraded from version 1.03 to 1.05.

=item *

C<diagnostics> has been upgraded from version 1.19 to 1.22.

It now renders pod links slightly better, and has been taught to find
descriptions for messages that share their descriptions with other
messages.

=item *

C<Digest::MD5> has been upgraded from version 2.39 to 2.51.

It is now safe to use this module in combination with threads.

=item *

C<Digest::SHA> has been upgraded from version 5.47 to 5.61.

C<shasum> now more closely mimics C<sha1sum>/C<md5sum>.

C<Addfile> accepts all POSIX filenames.

New SHA-512/224 and SHA-512/256 transforms ref. NIST Draft FIPS 180-4 (February 2011)

=item *

C<Dumpvalue> has been upgraded from version 1.13 to 1.15.

=item *

C<DynaLoader> has been upgraded from version 1.10 to 1.12.

It fixes a buffer overflow when passed a very long file name.

It no longer inherits from AutoLoader; hence it no longer
produces weird error messages for unsuccessful method calls on classes that
inherit from DynaLoader [perl #84358].

=item *

C<Encode> has been upgraded from version 2.39 to 2.42.

Now, all 66 Unicode non-characters are treated the same way U+FFFF has
always been treated; if it was disallowed, all 66 are disallowed; if it
warned, all 66 warn.

=item *

C<Env> has been upgraded from version 1.01 to 1.02.

=item *

C<Errno> has been upgraded from version 1.11 to 1.13.

The implementation of C<Errno> has been refactored to use about 55% less memory.
There should be no user-visible changes.

On some platforms with unusual header files, like Win32/gcc using mingw64
headers, some constants which weren't actually error numbers have been exposed
by C<Errno>.  This has been fixed [perl #77416].

=item *

C<Exporter> has been upgraded from version 5.64_01 to 5.64_03.

Exporter no longer overrides C<$SIG{__WARN__}> [perl #74472]

=item *

C<ExtUtils::CBuilder> has been upgraded from 0.27 to 0.280201.

Handle C and C++ compilers separately.

Preserves exit status on VMS.

=item *

C<ExtUtils::Command> has been upgraded from version 1.16 to 1.17.

=item *

C<ExtUtils::Constant> has been upgraded from 0.22 to 0.23.

The C<AUTOLOAD> helper code generated by C<ExtUtils::Constant::ProxySubs>
can now C<croak> for missing constants, or generate a complete C<AUTOLOAD>
subroutine in XS, allowing simplification of many modules that use it.
(C<Fcntl>, C<File::Glob>, C<GDBM_File>, C<I18N::Langinfo>, C<POSIX>, C<Socket>)

C<ExtUtils::Constant::ProxySubs> can now optionally push the names of all
constants onto the package's C{@EXPORT_OK}. This has been used to replace
less space-efficient code in C<B>, helping considerably shrink the size of its
shared object.

=item *

C<ExtUtils::Constant::Utils> has been upgraded from 0.02 to 0.03.

Refactoring and fixing of backcompat code, preparing for resynchronisation
with CPAN.

=item *

C<ExtUtils::Embed> has been upgraded from 1.28 to 1.30.

=item *

C<ExtUtils::MakeMaker> has been upgraded from version 6.56 to 6.57_05.

=item *

C<ExtUtils::Manifest> has been upgraded from version 1.57 to 1.58.

=item *

C<ExtUtils::ParseXS> has been upgraded from 2.21 to 2.2208.

=item *

C<Fcntl> has been upgraded from 1.06 to 1.11.

=item *

C<File::Copy> has been downgraded from version 2.17 to 2.21.

An extra stanza was added explaining behaviours when the copy destination
already exists and is a directory.

=item *

C<File::DosGlob> has been upgraded from version 1.01 to 1.03.

It allows patterns containing literal parentheses (they no longer need to
be escaped). On Windows, it no longer adds an extra F<./> to the file names
returned when the pattern is a relative glob with a drive specification,
like F<c:*.pl> [perl #71712].

=item *

C<File::Fetch> has been upgraded from version 0.24 to 0.32.

C<HTTP::Lite> is now supported for 'http' scheme.

The C<fetch> utility is supported on FreeBSD, NetBSD and
Dragonfly BSD for the C<http> and C<ftp> schemes.

=item *

C<File::Find> has been upgraded from version 1.15 to 1.18.

It improves handling of backslashes on Windows, so that paths such as
F<c:\dir\/file> are no longer generated [perl #71710].

=item *

C<feature> has been upgraded from 1.16 to 1.19.

Documentation and test updates for the C<unicode_strings> feature.
See L</Full functionality for C<use feature 'unicode_strings'>>.

=item *

C<File::CheckTree> has been upgraded from 4.4 to 4.41.

=item *

C<File::Glob> has been upgraded from 1.07 to 1.11.

=item *

C<File::stat> has been upgraded from 1.02 to 1.04.

The C<-x> and C<-X> file test operators now work correctly under the root
user.

=item *

C<Filter::Simple> has been upgraded from version 0.84 to 0.85.

=item *

C<GDBM_File> has been upgraded from 1.10 to 1.13.

This fixes a memory leak when DBM filters are used.

=item *

C<Hash::Util> has been upgraded from 0.07 to 0.10.

Hash::Util now enables "no warnings 'uninitialized'" to suppress spurious
warnings from undefined hash values (RT #74280).

=item *

C<Hash::Util::FieldHash> has been upgraded from 1.04 to 1.07.

=item *

C<I18N::Collate> has been upgraded from 1.01 to 1.02.

=item *

C<I18N::Langinfo> has been upgraded from version 0.03 to 0.07.

C<langinfo()> now defaults to using C<$_> if there is no argument given, just
like the documentation always claimed it did.

=item *

C<I18N::LangTags> has been upgraded from version 0.35 to 0.35_01.

=item *

C<if> has been upgraded from version 0.05 to 0.0601.

=item *

C<IO> has been upgraded from version 1.25_02 to 1.25_04.

=item *

The IO-Compress distribution has been upgraded from version 2.024 to 2.033.

=item *

C<IO::Select> has been upgraded from version 1.17 to 1.18.

It now allows IO::Handle objects (and objects in derived classes) to be
removed from an IO::Select set even if the underlying file descriptor is
closed or invalid.

=item *

C<IO::Socket> has been upgraded from version 1.31 to 1.32.

C<getsockopt> and C<setsockopt> are now documented.

=item *

C<IPC::Cmd> has been upgraded from version 0.54 to 0.68.

Resolves an issue with splitting Win32 command lines.

=item *

C<IPC::Open3> has been upgraded from 1.05 to 1.08.

C<open3> now produces an error if the C<exec> call fails, allowing this
condition to be distinguished from a child process that exited with a
non-zero status [perl #72016].

The internal C<xclose> routine now knows how to handle file descriptors, as
documented, so duplicating STDIN in a child process using its file
descriptor now works [perl #76474].

=item *

C<IPC::SysV> has been upgraded from version 2.01 to 2.03.

=item *

C<lib> has been upgraded from version 0.62 to 0.63.

=item *

The Locale-Codes distribution has been upgraded from version 2.07 to 3.16.

Locale::Country, Locale::Language and Locale::Currency were updated from
3.12 to 3.13 of the Locale-Codes distribution to include locale code changes.

Adds some codes.

=item *

C<Locale::Maketext> has been upgraded from version 1.14 to 1.17.

Locale::Maketext guts have been merged back into the main module
and adds external cache support

It fixes an infinite loop in C<Locale::Maketext::Guts::_compile()> when
working with tainted values (CPAN RT #40727).

C<< ->maketext >> calls will now backup and restore C<$@> so that error
messages are not suppressed (CPAN RT #34182).

=item *

C<Log::Message> has been upgraded from version 0.02 to 0.04.

=item *

C<Log::Message::Simple> has been upgraded from version 0.06 to 0.08.

=item *

C<Math::BigInt> has been upgraded from version 1.89_01 to 1.994.

This fixes, among other things, incorrect results when computing binomial
coefficients [perl #77640].

This prevents C<sqrt($int)> from crashing under C<use bigrat;>
[perl #73534].

=item *

C<Math::BigInt::FastCalc> has been upgraded from version 0.19 to 0.28.

=item *

C<Math::BigRat> has been upgraded from version 0.24 to 0.26_01.

=item *

C<Memoize> has been upgraded from version 1.01_03 to 1.02.

=item *

C<MIME::Base64> has been upgraded from 3.08 to 3.13.

Includes new functions to calculate the length of encoded and decoded
base64 strings.

Now provides C<encode_base64url> and C<decode_base64url> functions to process
the base64 scheme for "URL applications".

=item *

C<Module::Build> has been upgraded from version 0.3603 to 0.3800.

A notable change is the deprecation of several modules.
Module::Build::Version has been deprecated and Module::Build now relies
directly upon L<version>.  Module::Build::ModuleInfo has been deprecated in
favor of a standalone copy of it called L<Module::Metadata>.
Module::Build::YAML has been deprecated in favor of L<CPAN::Meta::YAML>.

Module::Build now also generates META.json and MYMETA.json files
in accordance with version 2 of the CPAN distribution metadata specification,
L<CPAN::Meta::Spec>.  The older format META.yml and MYMETA.yml files are
still generated, as well.

=item *

C<Module::CoreList> has been upgraded from version 2.29 to XXX.

Besides listing the updated core modules of this release, it also stops listing
the C<Filespec> module. That module never existed in core. The scripts
generating C<Module::CoreList> confused it with C<VMS::Filespec>, which actually
is a core module, since the time of perl 5.8.7.

=item *

C<Module::Load> has been upgraded from version 0.16 to 0.18.

=item *

C<Module::Load::Conditional> has been upgraded from version 0.34 to 0.40.

=item *

C<Module::Metadata> has been upgraded from version 1.000003 to 1.000004.

XXX This is not listed in corelist for 5.12.0. When was it added?

=item *

C<mro> has been upgraded from version 1.02 to 1.06.

C<next::method> I<et al.> now take into account that every class inherits
from UNIVERSAL [perl #68654].

=item *

C<NDBM_File> has been upgraded from 1.08 to 1.11.

This fixes a memory leak when DBM filters are used.

=item *

C<NEXT> has been upgraded from version 0.64 to 0.65.

=item *

C<ODBM_File> has been upgraded from 1.08 to 1.09.

This fixes a memory leak when DBM filters are used.

=item *

C<Net::Ping> has been upgraded from 2.36 to 2.37.

=item *

C<ODBM_File> has been upgraded from 1.07 to 1.10.

=item *

C<Object::Accessor> has been upgraded from version 0.36 to 0.38.

=item *

C<open> has been upgraded from version 1.07 to 1.08.

=item *

C<Opcode> has been upgraded from 1.15 to 1.18.

=item *

C<overload> has been upgraded from 1.11 to 1.12.

C<overload::Method> can now handle subroutines that are themselves blessed
into overloaded classes [perl #71998].

Avoid a taint problem in use of sprintf.

The documentation has greatly improved. See L</Documentation> below.

=item *

C<Params::Check> has been upgraded from version 0.26 to 0.28.

=item *

C<parent> has been upgraded from version 0.223 to 0.225.

=item *

C<Parse::CPAN::Meta> has been upgraded from version 1.40 to 1.4401.

The latest Parse::CPAN::Meta can now read YAML or JSON files using
L<CPAN::Meta::YAML> and L<JSON::PP>, which are now part of the Perl core.

=item *

The PathTools distribution has been upgraded from version 3.31 to 3.34.

Various issues in L<File::Spec::VMS> have been fixed. (5.13.4)

=item *

C<PerlIO::encoding> has been upgraded from 0.12 to 0.14.

=item *

C<PerlIO::scalar> has been upgraded from 0.07 to 0.11.

A C<read> after a C<seek> beyond the end of the string no longer thinks it
has data to read [perl #78716].

=item *

C<PerlIO::via> has been upgraded from 0.09 to 0.11.

=item *

The podlators distribution has been upgraded from version 2.3.1 to 2.4.0.

=item *

C<Pod::LaTeX> has been upgraded from version 0.58 to 0.59.

=item *

C<Pod::Simple> has been upgraded from 3.14 to 3.15

Includes various fixes to C<HTML> and C<XHTML> handling.

=item *

C<POSIX> has been upgraded from 1.19 to 1.23.

It now includes constants for POSIX signal constants.

=item *

C<re> has been upgraded from version 0.11 to 0.15.

New C<use re "/flags"> pragma

Enforce that C</d>, C</u>, and C</l> are mutually exclusive.

C<re> has been upgraded from version 0.16 to 0.17.

It now supports the double-a flag: C<use re '/aa';>

The C<regmust> function used to crash when called on a regular expression
belonging to a pluggable engine. Now it has been disabled for those.

C<regmust> no longer leaks memory.

=item *

C<Safe> has been upgraded from version 2.25 to 2.29.

This fixes a possible infinite loop when looking for coderefs.

It adds C<&version::vxs::VCMP> to the default share.

=item *

C<SDBM_File> has been upgraded from 1.06 to 1.08.

=item *

C<SelfLoader> has been upgraded from 1.17 to 1.18.

It now works in taint mode [perl #72062].

=item *

C<sigtrap> has been upgraded from version 1.04 to 1.05.

It no longer tries to modify read-only arguments when generating a
backtrace [perl #72340].

=item *

C<Socket> has been upgraded from version 1.87 to XXX.

It has several new functions for handling IPv6 addresses. (from 5.13.8)

It provides new affordances for IPv6,
including implementations of the C<Socket::getaddrinfo()> and
C<Socket::getnameinfo()> functions, along with related constants.

=item *

C<Storable> has been upgraded from version 2.22 to 2.27.

Includes performance improvement for overloaded classes.

=item *

C<Storable> has been upgraded from 2.24 to 2.25.

This adds support for serialising code references that contain UTF-8 strings
correctly. The Storable minor version number changed as a result, meaning that
Storable users who set C<$Storable::accept_future_minor> to a C<FALSE> value
will see errors (see L<Storable/FORWARD COMPATIBILITY> for more details).

Freezing no longer gets confused if the Perl stack gets reallocated
during freezing [perl #80074].

=item *

C<Sys::Hostname> has been upgraded from 1.11 to 1.14.

=item *

C<Term::ANSIColor> has been upgraded from version 2.02 to 3.00.

=item *

C<Term::UI> has been upgraded from version 0.20 to 0.26.

=item *

C<Test::Harness> has been upgraded from version 3.17 to 3.23.

The core update from Test-Harness 3.17 to 3.21 fixed some things, but
also L<introduced a known problem|/"Known Problems"> with argument
passing to non-Perl tests. (5.13.3)

=item *

C<Test::Simple> has been upgraded from version 0.94 to 0.98.

Among many other things, subtests without a C<plan> or C<no_plan> now have an
implicit C<done_testing()> added to them.

=item *

C<Thread::Queue> has been upgraded from version 2.11 to 2.12.

=item *

C<Thread::Semaphore> has been upgraded from version 2.09 to 2.12.

Added new methods -E<gt>down_nb() and -E<gt>down_force() at the suggestion
of Rick Garlick.

Refactored methods to skip argument validation when no argument is supplied.

=item *

C<threads> has been upgraded from version 1.75 to 1.82.

=item *

C<threads::shared> has been upgraded from version 1.32 to 1.36.

=item *

C<Tie::Hash> has been upgraded from version 1.03 to 1.04.

Calling C<< Tie::Hash-E<gt>TIEHASH() >> used to loop forever.  Now it C<croak>s.

=item *

C<Tie::Hash::NamedCapture> has been upgraded from version 0.06 to 0.08.

Some of the Perl code has been converted to XS for efficency's sake.

=item *

C<Tie::RefHash> has been upgraded from version 1.38 to 1.39.

=item *

C<Time::HiRes> has been upgraded from version 1.9719 to 1.9721.

=item *

C<Time::Local> has been upgraded from version 1.1901_01 to 1.2000.

=item *

C<Time::Piece> has been upgraded from version 1.15_01 to 1.20_01.

=item *

C<Unicode::Collate> has been upgraded from version 0.52_01 to 0.73.

Includes Unicode Collation Algorithm 18

Among other things, it is now using UCA Revision 20 (based on Unicode 5.2.0) and
supports a couple of new locales.

U::C::Locale newly supports locales: ar, be, bg, de__phonebook, hu, hy, kk, mk, nso, om, 
tn, vi, hr, ig, ru, sq, se, sr, to and uk

This release newly adds locales C<ja> C<ko> and C<zh> and its variants 
( C<zh__big5han>, C<zh__gb2312han>, C<zh__pinyin>, C<zh__stroke> ).

Supported UCA_Version 22 for Unicode 6.0.0.

The following modules have been added:

C<Unicode::Collate::CJK::Big5> for C<zh__big5han> which makes 
tailoring of CJK Unified Ideographs in the order of CLDR's big5han ordering.

C<Unicode::Collate::CJK::GB2312> for C<zh__gb2312han> which makes
tailoring of CJK Unified Ideographs in the order of CLDR's gb2312han ordering.

C<Unicode::Collate::CJK::JISX0208> which makes tailoring of 6355 kanji 
(CJK Unified Ideographs) in the JIS X 0208 order.

C<Unicode::Collate::CJK::Korean> which makes tailoring of CJK Unified Ideographs 
in the order of CLDR's Korean ordering.

C<Unicode::Collate::CJK::Pinyin> for C<zh__pinyin> which makes
tailoring of CJK Unified Ideographs in the order of CLDR's pinyin ordering.

C<Unicode::Collate::CJK::Stroke> for C<zh__stroke> which makes
tailoring of CJK Unified Ideographs in the order of CLDR's stroke ordering.

DUCET has been updated for Unicode 6.0.0 as Collate/allkeys.txt and
the default UCA_Version is 22.

This also sees the switch from using the pure-perl version of this
module to the XS version.

=item *

C<Unicode::Normalize> has been upgraded from version 1.03 to 1.10.

=item *

C<Unicode::UCD> has been upgraded from version 0.27 to 0.32.

Add info about named sequence alternatives.

Don't use C<CompositionExclusions.txt>.

This includes a number of bug fixes:

=over 4

=item charinfo()

=over 4

=item *

It is now updated to Unicode Version 6 with Corrigendum #8, except,
as with Perl 5.14, the code point at U+1F514 has no name.

=item *

The Hangul syllable code points have the correct names, and their
decompositions are always output without requiring L<Lingua::KO::Hangul::Util>
to be installed.

=item *

The CJK (Chinese-Japanese-Korean) code points U+2A700 - U+2B734
and U+2B740 - 2B81D are now properly handled.

=item *

The numeric values are now output for those CJK code points that have them.

=item *

The names that are output for code points with multiple aliases are now the
corrected ones.

=back

=item charscript()

This now correctly returns "Unknown" instead of C<undef> for the script
of a code point that hasn't been assigned another one.

=item charblock()

This now correctly returns "No_Block" instead of C<undef> for the block
of a code point that hasn't been assigned to another one.

=back

Added new function C<Unicode::UCD::num()>.  This function will return the
numeric value of the string passed it; C<undef> if the string in its
entirety has no safe numeric value.

To be safe, a string must be a single character which has a numeric
value, or consist entirely of characters that match \d, coming from the
same Unicode block of digits.  Thus, a mix of  Bengali and Western
digits would be considered unsafe, as well as a mix of half- and
full-width digits, but strings consisting entirely of Devanagari digits
or of "Mathematical Bold" digits would would be safe.

=item *

C<version> has been upgraded from 0.82 to 0.88.

Modify export logic for C<is_strict> and C<is_lax>.

=item *

C<warnings> and C<warnings::register> have been upgraded from version 1.09
to 1.11 and from version 1.01 to 1.02 respectively.

Calling C<use warnings> without arguments is now significantly more efficient.

It is now possible to register warning categories other than the names of
packages using C<warnings::register>.  See L<perllexwarn> for more information.

=item *

C<VMS::DCLsym> has been upgraded from version 1.03 to 1.05.

Two bugs have been fixed [perl #84086]:

The symbol table name was lost when tying a hash, due to a thinko in
C<TIEHASH>. The result was that all tied hashes interacted with the
local symbol table.

Unless a symbol table name had been explicitly specified in the call
to the constructor, querying the special key ':LOCAL' failed to
identify objects connected to the local symbol table.

=item *

C<Win32> has been upgraded from version 0.39 to 0.44.

Add several functions. (5.13.8)

Corrections to names returned by C<Win32::GetOSName> and
C<Win32::GetOSDisplayName>.

=item *

C<XSLoader> has been upgraded from version 0.10 to 0.11.

=back

=head2 Dual-life Modules and Pragmata

These modules were formerly distributed only in the Perl core
distribution, and are now dual-lifed (meaning they are now also available
separately on CPAN):

=over 4

=item *

C<autouse>

=item *

C<Devel::SelfStubber>

=item *

C<Dumpvalue>

=item *

C<Env>

=item *

C<File::CheckTree>

=item *

C<I18N::Collate>

=back

=head2 Removed Modules and Pragmata

The following modules have been removed from the core distribution, and if
needed should be installed from CPAN instead.

=over

=item C<Class::ISA>

=item C<Pod::Plainer>

=item C<Switch>

=back

The removal of C<Shell> has been deferred until after 5.14, as the
implementation of C<Shell> shipped with 5.12.0 did not correctly issue the
warning that it was to be removed from core.

=head1 Documentation

XXX Changes to files in F<pod/> go here.  Consider grouping entries by
file and be sure to link to the appropriate page, e.g. L<perlfunc>.

=head2 New Documentation

=head3 perlgpl

L<perlgpl> has been updated to contain GPL version 1, as is included in the
F<README> distributed with perl.

=head3 L<perl5121delta>

The Perl 5.12.1 perldelta file was added from the Perl maintenance branch

=head3 L<perlpodstyle>

New style guide for POD documentation,
split mostly from the NOTES section of the pod2man man page.

( This was added to C<v5.13.6> but was not documented with that release ).

=head2 Changes to Existing Documentation

=head3 L<perlmodlib>

The perlmodlib page that came with Perl 5.12.0 was missing a lot of
modules, due to a bug in the script that generates the list. This has been
fixed [perl #74332].

=head3 Replace wrong tr/// table in perlebcdic.pod

perlebcdic.pod contains a helpful table to use in tr/// to convert
between EBCDIC and Latin1/ASCII.  Unfortunately, the table was the
inverse of the one it describes, though the code that used the table
worked correctly for the specific example given.

The table has been changed to its inverse, and the sample code changed
to correspond, as this is easier for the person trying to follow the
instructions since deriving the old table is somewhat more complicated.

The table has also been changed to hex from octal, as that is more the norm
these days, and the recipes in the pod altered to print out leading
zeros to make all the values the same length, as the table that they can
generate has them (5f26d5).

=head3 Document tricks for user-defined casing

perlunicode.pod now contains an explanation of how to override, mangle
and otherwise tweak the way perl handles upper, lower and other case
conversions on unicode data, and how to provide scoped changes to alter
one's own code's behaviour without stomping on anybody else (71648f).

=head3 Document $# and $* as removed and clarify $#array usage

$# and $* were both disabled as of perl5 version 10; this release adds
documentation to that effect, a description of the results of continuing
to try and use them, and a note explaining that $# can also function as a
sigil in the $#array form (7f315d2).

=head3 INSTALL explicitly states the requirement for C89

This was already true but it's now Officially Stated For The Record (51eec7).

=head3 No longer advertise Math::TrulyRandom

This module hasn't been updated since 1996 so we can't recommend it any more
(83918a).

=head3 perlfaq synchronised to upstream

The FAQ has been updated to commit
37550b8f812e591bcd0dd869d61677dac5bda92c from the perlfaq repository
at git@github.com:briandfoy/perlfaq.git

=head3 General changes

=over

=item *

Octal character escapes in documentation now prefer a three-digit octal
escape or the new C<\o{...}> escape as they have more consistent behavior
in different contexts than other forms. (ce7b6f0) (d8b950d) (e1f120a)

=item *

Documentation now standardizes on the term 'capture group' over 'buffer'
in regular expression documentation (c27a5cf)

=back

=head3 L<perlfunc>

=over

=item *

Added cautionary note about "no VERSION" (e0de7c2)

=item *

Added additional notes regarding srand when forking (d460397)

=back

=head3 L<perlop>

=over 4

=item *

Improved documentation of unusual character escapes (4068718, 9644846)

=item *

Clarified how hexadecimal escapes are interpreted, with particular
attention to the treatment of invalid characters (9644846)

=back

=head3 L<perlrun>

=over

=item *

Clarified the behavior of the C<-0NNN> switch for C<-0400> or higher (7ba31cb)

=back

=head3 L<perlpolicy>

=over

=item *

Added the policy on compatibility and deprecation along with definitions of
terms like "deprecation" (70e4a83)

=back

=head3 L<perlre>

=over

=item *

Added examples of the perils of not using \g{} when there are more
than nine back-references (9d86067)

=back

=head3 L<perltie>

=over

=item *

Updated some examples for modern Perl style (67d00dd)

=back

=head3 L<perldiag>

=over 4

=item *

The following existing diagnostics are now documented:

=over 4

=item *

L<Ambiguous use of %c resolved as operator %c|perldiag/"Ambiguous use of %c resolved as operator %c">

=item *

L<Ambiguous use of %c{%s} resolved to %c%s|perldiag/"Ambiguous use of %c{%s} resolved to %c%s">

=item *

L<Ambiguous use of %c{%s%s} resolved to %c%s%s|perldiag/"Ambiguous use of %c{%s%s} resolved to %c%s%s">

=item *

L<Ambiguous use of -%s resolved as -&%s()|perldiag/"Ambiguous use of -%s resolved as -&%s()">

=item *

L<Invalid strict version format (%s)|perldiag/"Invalid strict version format (%s)">

=item *

L<Invalid version format (%s)|perldiag/"Invalid version format (%s)">

=item *

L<Invalid version object|perldiag/"Invalid version object">

=back

=back

=head3 L<perlport>

=over 4

=item *

Documented a L<limitation|perlport/alarm> of L<alarm()|perlfunc/"alarm SECONDS">
on Win32.

=back

=head3 L<perlre>

=over 4

=item *

Minor fix to a multiple scalar match example.

=back

=head3 L<perlapi>

=over 4

=item *

Many of the optree construction functions are now documented.

=back

=head3 L<perlbook>

=over 4

=item *

Expanded to cover many more popular books.

=back

=head3 L<perlfaq>

=over 4

=item *

L<perlfaq>, L<perlfaq2>, L<perlfaq4>, L<perlfaq5>, L<perlfaq6>, L<perlfaq8>, and
L<perlfaq9> have seen various updates and modernizations.

=back

=head3 L<perlapi>

=over 4

=item *

The documentation for the C<SvTRUE> macro was simply wrong in stating that
get-magic is not processed. It has been corrected.

=back

=head3 L<perlvar>

L<perlvar> reorders the variables and groups them by topic. Each variable
introduced after Perl 5.000 notes the first version in which it is 
available. L<perlvar> also has a new section for deprecated variables to
note when they were removed.

=head3 blah blah blah

Array and hash slices in scalar context are now documented in L<perldata>.

=head3 blah blah blah

L<perlform> and L<perllocale> have been corrected to state that
C<use locale> affects formats.

=head3 All documentation

=over

=item *

Numerous POD warnings were fixed.

=item *

Many, many spelling errors and typographical mistakes were corrected throughout Perl's core.

=back

=head3 C<perlhack>

=over 4

=item *

C<perlhack> was extensively reorganized.

=back

=head3 C<perlfunc>

=over 4

=item *

It has now been documented that C<ord> returns 0 for an empty string.

=back

=head3 L<overload>

=over 4

=item *

L<overload>'s documentation has practically undergone a rewrite. It
is now much more straightforward and clear.

=back

=head3 L<perlhack> and perlrepository

=over 4

=item *

The L<perlhack> and perlrepository documents have been heavily edited and
split up into several new documents.

The L<perlhack> document is now much shorter, and focuses on the Perl 5
development process and submitting patches to Perl. The technical content has
been moved to several new documents, L<perlsource>, L<perlinterp>,
L<perlhacktut>, and L<perlhacktips>. This technical content has only been
lightly edited.

The perlrepository document has been renamed to L<perlgit>. This new document
is just a how-to on using git with the Perl source code. Any other content
that used to be in perlrepository has been moved to perlhack.

=back

=head3 L<perlfunc>

=over 4

=item *

The documentation for the C<map> function now contains more examples,
see B<perldoc -f map> (f947627)

=back

=head3 L<perlfaq4>

=over 4

=item *

Examples in L<perlfaq4> have been updated to show the use of
L<Time::Piece>. (9243591)

=back

=head3 Miscellaneous

=over 4

=item *

Many POD related RT bugs and other issues which are too numerous to
enumerate have been solved by Michael Stevens.

=back

=head1 Diagnostics

The following additions or changes have been made to diagnostic output,
including warnings and fatal error messages.  For the complete list of
diagnostic messages, see L<perldiag>.

=head2 New Diagnostics

=over

=item Parsing code internal error (%s)

New fatal error produced when parsing code supplied by an extension violated the
parser's API in a detectable way.

=item Use of qw(...) as parentheses is deprecated

See L</"Use of qw(...) as parentheses"> for details.

=item Using !~ with %s doesn't make sense

This message was actually added in
5.13.2, but was omitted from perldelta. It now applies also to the C<y///>
operator, and has been documented.

=item Closure prototype called

There is a new "Closure prototype called" error [perl #68560].

=item Operation "%s" returns its argument for ...

Performing an operation requiring Unicode semantics (such as case-folding)
on a Unicode surrogate or a non-Unicode character now triggers a warning:
'Operation "%s" returns its argument for ...'.

=item "\b{" is deprecated; use "\b\{" instead

=item "\B{" is deprecated; use "\B\{" instead

Use of an unescaped "{" immediately following a C<\b> or C<\B> is now
deprecated so as to reserve its use for Perl itself in a future release.

=item regcomp: Add warning if \p is used under locale. (fb2e24c)

C<\p> implies Unicode matching rules, which are likely going to be
different than the locale's.

=item panic: gp_free failed to free glob pointer - something is repeatedly re-creating entries

This new error is triggered if a destructor called on an object in a
typeglob that is being freed creates a new typeglob entry containing an
object with a destructor that creates a new entry containing an object....

=item refcnt: fd %d%s

This new error only occurs if a internal consistency check fails when a
pipe is about to be closed.

=item Regexp modifier "/%c" may not appear twice

(F syntax) The regular expression pattern had one of the mutually exclusive
modifiers repeated.  Remove all but one of the occurrences.

=item Regexp modifiers "/%c" and "/%c" are mutually exclusive

(F syntax) The regular expression pattern had more than one of the mutually
exclusive modifiers.  Retain only the modifier that is supposed to be there.

=item Insecure user-defined property %s

(F) Perl detected tainted data when trying to compile a regular
expression that contains a call to a user-defined character property
function, i.e. C<\p{IsFoo}> or C<\p{InFoo}>.
See L<perlunicode/User-Defined Character Properties> and L<perlsec>.

=back

=head2 Changes to Existing Diagnostics

=over 4

=item *

The "Variable $foo is not imported" warning that precedes a
C<strict 'vars'> error has now been assigned the "misc" category, so that
C<no warnings> will suppress it [perl #73712].

=item *

C<warn> and C<die> now produce 'Wide character' warnings when fed a
character outside the byte range if STDERR is a byte-sized handle.

=item *

The 'Layer does not match this perl' error message has been replaced with
these more helpful messages:

=over 4

=item *

PerlIO layer function table size (%d) does not match size expected by this
perl (%d)

=item *

PerlIO layer instance size (%d) does not match size expected by this perl
(%d)

=back

[perl #73754]

=item *

The "Found = in conditional" warning that is emitted when a constant is
assigned to a variable in a condition is now withheld if the constant is
actually a subroutine or one generated by C<use constant>, since the value
of the constant may not be known at the time the program is written
[perl #77762].

=item *

Previously, if none of the C<gethostbyaddr>, C<gethostbyname> and
C<gethostent> functions were implemented on a given platform, they would
all die with the message 'Unsupported socket function "gethostent" called',
with analogous messages for C<getnet*> and C<getserv*>. This has been
corrected.

=item *

The warning message about regex unrecognized escapes passed through is
changed to include any literal '{' following the 2-char escape.  e.g.,
"\q{" will include the { in the message as part of the escape
(216bfc0).

=item *

C<binmode $fh, ':scalar'> no longer warns (8250589)

Perl will now no longer produce this warning:

    $ perl -we 'open my $f, ">", \my $x; binmode $f, "scalar"'
    Use of uninitialized value in binmode at -e line 1.

=back

=head1 Utility Changes

=head3 L<perldb>

=over

=item *

The remote terminal works after forking and spawns new sessions - one
for each forked process (11653f7)

=item *

Uses the less pager path from Config instead of searching for it (bf320d6)

=back

=head3 L<h2ph>

=over 4

=item *

The use of a deprecated C<goto> construct has been removed [perl #74404].

=back

=head3 L<ptargrep>

=over 4

=item *

L<ptargrep> is a utility to apply pattern matching to the contents of files 
in a tar archive. It comes with C<Archive::Tar>.

=back

=head3 C<perlbug>

=over 4

=item *

C<perlbug> now looks in the EMAIL environment variable for a return address
if the REPLY-TO and REPLYTO variables are empty.

=item *

C<perlbug> did not previously generate a From: header, potentially
resulting in dropped mail. Now it does include that header.

=back

=head3 C<buildtoc>

=over 4

=item *

F<pod/buildtoc> has been modernized and can now be used to test the
well-formedness of F<pod/perltoc.pod> automatically.

=back

=head3 L<perlbug>

=over 4

=item *

[perl #82996] Use the user's from address as return-path in perlbug

Many systems these days don't have a valid Internet domain name and
perlbug@perl.org does not accept email with a return-path that does
not resolve. Therefore pass the user's address to sendmail so it's
less likely to get stuck in a mail queue somewhere. (019cfd2)

=back

=head1 Configuration and Compilation

=over 4

=item *

Fix CCINCDIR and CCLIBDIR for mingw64 cross compiler to correctly be under
$(CCHOME)\mingw\include and \lib rather than immediately below $(CCHOME).

=item *

This means the 'incpath', 'libpth', 'ldflags', 'lddlflags' and
'ldflags_nolargefiles' values in Config.pm and Config_heavy.pl are now
set correctly (23ae7f).

=item *

Adjusted 'make test.valgrind' to account for cpan/dist/ext separation
(e07ce2e)

=item *

Compatibility with C<C++> compilers has been improved.

=item *

On compilers that support it, C<-Wwrite-strings> is now added to cflags by
default.

=item *

The C<Encode> module can now (once again) be included in a static Perl
build.  The special-case handling for this situation got broken in Perl
5.11.0, and has now been repaired.

=back

=head1 Testing

XXX Any significant changes to the testing of a freshly built perl should be
listed here.  Changes which create B<new> files in F<t/> go here as do any
large changes to the testing harness (e.g. when parallel testing was added).
Changes to existing files in F<t/> aren't worth summarising, although the bugs
that they represent may be covered elsewhere.

=over 4

=item *

F<t/harness> clears PERL5LIB, PERLLIB, PERL5OPT as t/TEST does (a2d3de1)

=item *

Many common testing routines were refactored into t/lib/common.pl

=item *

Several test files have been modernized to use Test::More

=item *

F<t/op/print.t> has been added to test implicit printing of C<$_>.

=item *

F<t/io/errnosig.t> has been added to test for restoration of of C<$!> when
leaving signal handlers.

=item *

F<t/op/tie_fetch_count.t> has been added to see if C<FETCH> is only called once
on tied variables.

=item *

F<lib/Tie/ExtraHash.t> has been added to make sure the, previously untested,
L<Tie::ExtraHash> keeps working.

=item *

F<t/re/overload.t> has been added to test against string corruption in pattern
matches on overloaded objects. This is a TODO test.

=item *

The new F<t/lib/universal.t> script tests the Internal::* functions and other
things in F<universal.c>.

=item *

A rare race condition in F<t/op/while_readdir.t> has been fixed, stopping it
from failing randomly when running tests in parallel.

=item *

The new F<t/op/leaky-magic.t> script tests that magic applied to variables in
the main packages does not affect other packages.

=item *

The script F<t/op/threads-dirh.t> has been added, which tests interaction
of threads and directory handles.

=item *

The new F<t/mro/isa_aliases.t> has been added, which tests that
C<*Foo::ISA = *Bar::ISA> works properly.

=item *

F<t/mro/isarev.t> has been added, which tests that C<PL_isarev> (accessible
at the Perl level via C<mro::get_isarev>) is updated properly.

=item *

F<t/run/switchd-78586.t> has been added, which tests that [perl #78586]
has been fixed (related to line numbers in the debugger).

=item *

C<lib/File/DosGlob.t> has been modernized and now uses C<Test::More>.

=item *

A new test script, C<t/porting/filenames.t>, makes sure that filenames and
paths are reasonably portable.

=item *

C<t/porting/diag.t> is now several orders of magnitude faster.

=item *

C<t/porting/buildtoc.t> now tests that the documentation TOC file is current and well-formed.

=item *

C<t/base/while.t> now tests the basics of a while loop with minimal dependencies.

=item *

C<t/cmd/while.t> now uses F<test.pl> for better maintainability.

=item *

C<t/op/split.t> now tests calls to C<split> without any pattern specified.

=item *

F<porting/FindExt.t> now skips all tests on a static (-Uusedl) build
of perl.

=item *

F<porting/FindExt.t> now passes on non-Win32 platforms when some
extensions are built statically.

=item *

The tests for C<split /\s/> and Unicode have been moved from
F<t/op/split.t> to the new F<t/op/split_unicode.t>.

=item *

F<t/re/re.t> has been moved to F<ext/re/t/re_funcs_u.t>.

=item *

The tests for [perl #72922] have been moved from F<t/re/qr.t> to the new
F<t/re/qr-72922.t>.

=item *

F<t/re/reg_unsafe.t> has been deleted and its only test moved to
F<t/re/pat_advanced.t>.

=back

=head1 Platform Support

XXX Any changes to platform support should be listed in the sections below.

[ Within the sections, list each platform as a =item entry with specific
changes as paragraphs below it. ]

=head2 New Platforms

XXX List any platforms that this version of perl compiles on, that previous
versions did not. These will either be enabled by new files in the F<hints/>
directories, or new subdirectories and F<README> files at the top level of the
source tree.

=over 4

=item AIX

Perl now builds on AIX 4.2.

=back

=head2 Discontinued Platforms

=over 4

=item MacOS Classic

Support for MacOS Classic within ExtUtils::MakeMaker was removed from Perl in
December 2004.  Vestigial MacOS Classic specific code has now been removed
from other core modules as well (8f8c2a4..c457df0)

=item Apollo DomainOS

The last vestiges of support for this platform have been excised from the
Perl distribution. It was officially discontinued in version 5.12.0. It had
not worked for years before that.

=item MacOS Classic

The last vestiges of support for this platform have been excised from the
Perl distribution. It was officially discontinued in an earlier version.

=back

=head2 Platform-Specific Notes

=head3 Recent OpenBSDs now use perl's malloc

OpenBSD E<gt> 3.7 has a new malloc implementation which is mmap based
and as such can release memory back to the OS; however for perl using
this malloc causes a substantial slowdown so we now default to using
perl's malloc instead (RT #75742) (9b58b5).

=head3 VMS

=over 4

=item *

Make C<PerlIOUnix_open> honour default permissions on VMS.

When C<perlio> became the default and C<unixio> became the default bottom layer,
the most common path for creating files from Perl became C<PerlIOUnix_open>,
which has always explicitly used C<0666> as the permission mask.

To avoid this, C<0777> is now passed as the permissions to C<open()>.  In the
VMS CRTL, C<0777> has a special meaning over and above intersecting with the
current umask; specifically, it allows Unix syscalls to preserve native default
permissions.

=back

=head3 Win32

t/io/openpid.t now uses the alarm() watchdog strategy for more
robustness (5732108)

=over 4

=item *

Fixed a possible hang in F<t/op/readline.t>.

=item *

Fixed build process for SDK2003SP1 compilers.

=item *

When using old 32-bit compilers, the define C<_USE_32BIT_TIME_T> will now be set
in C<$Config{ccflags}>. This improves portability when compiling XS extensions
using new compilers, but for a perl compiled with old 32-bit compilers.

=back

XXX A bunch of entries that need conversion to =head2 format (unless the
entries above change to =items):

=over

=item IRIX

Conversion of strings to floating-point numbers is now more accurate on
IRIX systems [perl #32380].

=item Mac OS X

Early versions of Mac OS X (Darwin) had buggy implementations of the
C<setregid>, C<setreuid>, C<setrgid> and C<setruid> functions, so perl
would pretend they did not exist.

These functions are now recognised on Mac OS 10.5 (Leopard; Darwin 9) and
higher, as they have been fixed [perl #72990].

=item OpenVOS

perl now builds again with OpenVOS (formerly known as Stratus VOS)
[perl #78132].

=item VMS

The shortening of symbols longer than 31 characters in the C sources is
now done by the compiler rather than by xsubpp (which could only do so
for generated symbols in XS code).

=item Windows

C<$Config{gccversion}> is now set correctly when perl is built using the
mingw64 compiler from L<http://mingw64.org> [perl #73754].

The build process proceeds more smoothly with mingw and dmake when
F<C:\MSYS\bin> is in the PATH, due to a C<Cwd> fix.

=item Windows

Directory handles are now properly cloned when threads are created. In perl
5.13.6, child threads simply stopped inheriting directory handles. In
previous versions, threads would share handles, resulting in crashes.

Support for building with Visual C++ 2010 is now underway, but is not yet
complete. See F<README.win32> for more details.

=item VMS

Record-oriented files (record format variable or variable with fixed control)
opened for write by the perlio layer will now be line buffered to prevent the
introduction of spurious line breaks whenever the perlio buffer fills up.

=item NetBSD

The NetBSD hints file has been changed to make the system's malloc the
default.

=item Windows

The option to use an externally-supplied C<crypt()>, or to build with no
C<crypt()> at all, has been removed.  Perl supplies its own C<crypt()>
implementation for Windows, and the political situation that required
this part of the distribution to sometimes be omitted is long gone.

=item Cygwin

=over

=item *

Updated MakeMaker to build man pages on cygwin.

=item *

Improved rebase behaviour

If a dll is updated on cygwin reuse the old imagebase address.
This solves most rebase errors, esp when updating on core dll's.
See L<http://www.tishler.net/jason/software/rebase/rebase-2.4.2.README> for more information.

=item *

Support the standard cyg dll prefix, which is e.g. needed for FFI's.

=item *

Updated build hints file

=back


=item Solaris

DTrace is now supported on Solaris. There used to be build failures, but
these have been fixed [perl #73630].

=item Windows

=over 4

=item *

The C<test-prep> build target now depends on F<pod/perltoc.pod> to allow the
F<t/porting/buildtoc.t> test to run successfully.

=back

=item MirBSD

=over 4

=item *

[perl #82988] Skip hanging taint.t test on MirBSD 10 (1fb83d0)

Skip a hanging test under MirBSD that was already being skipped under
OpenBSD.

=item *

Previously if you build perl with a shared libperl.so on MirBSD (the
default config), it will work up to the installation; however, once
installed, it will be unable to find libperl. Treat path handling
like in the other BSD dialects.

=back

=back

=head1 Internal Changes

=head2 New APIs

=head2 CLONE_PARAMS structure added to ease correct thread creation

Modules that create threads should now create C<CLONE_PARAMS> structures
by calling the new function C<Perl_clone_params_new()>, and free them with
C<Perl_clone_params_del()>. This will ensure compatibility with any future
changes to the internals of the C<CLONE_PARAMS> structure layout, and that
it is correctly allocated and initialised.

=head2 API function to parse statements

The C<parse_fullstmt> function has been added to allow parsing of a single
complete Perl statement.  See L<perlapi> for details.

=head2 API functions for accessing the runtime hinthash

A new C API for introspecting the hinthash C<%^H> at runtime has been added.
See C<cop_hints_2hv>, C<cop_hints_fetchpvn>, C<cop_hints_fetchpvs>,
C<cop_hints_fetchsv>, and C<hv_copy_hints_hv> in L<perlapi> for details.

=head2 C interface to C<caller()>

The C<caller_cx> function has been added as an XSUB-writer's equivalent of
C<caller()>.  See L<perlapi> for details.

=head2 Custom per-subroutine check hooks

XS code in an extension module can now annotate a subroutine (whether
implemented in XS or in Perl) so that nominated XS code will be called
at compile time (specifically as part of op checking) to change the op
tree of that subroutine.  The compile-time check function (supplied by
the extension module) can implement argument processing that can't be
expressed as a prototype, generate customised compile-time warnings,
perform constant folding for a pure function, inline a subroutine
consisting of sufficiently simple ops, replace the whole call with a
custom op, and so on.  This was previously all possible by hooking the
C<entersub> op checker, but the new mechanism makes it easy to tie the
hook to a specific subroutine.  See L<perlapi/cv_set_call_checker>.

To help in writing custom check hooks, several subtasks within standard
C<entersub> op checking have been separated out and exposed in the API.

=head2 Improved support for custom OPs

Custom ops can now be registered with the new C<custom_op_register> C
function and the C<XOP> structure. This will make it easier to add new
properties of custom ops in the future. Two new properties have been added
already, C<xop_class> and C<xop_peep>.

C<xop_class> is one of the OA_*OP constants, and allows L<B> and other
introspection mechanisms to work with custom ops that aren't BASEOPs.
C<xop_peep> is a pointer to a function that will be called for ops of this
type from C<Perl_rpeep>.

See L<perlguts/Custom Operators> and L<perlapi/Custom Operators> for more
detail.

The old C<PL_custom_op_names>/C<PL_custom_op_descs> interface is still
supported but discouraged.

=head2 Changes to existing APIs

XXX This probably contains also internal changes unrelated to APIs. It
needs to be sorted out. Maybe we also need an ‘Other Changes’ or ‘Really
Internal Changes’ section.

=over 4

=item *

The protocol for unwinding the C stack at the last stage of a C<die>
has changed how it identifies the target stack frame.  This now uses
a separate variable C<PL_restartjmpenv>, where previously it relied on
the C<blk_eval.cur_top_env> pointer in the C<eval> context frame that
has nominally just been discarded.  This change means that code running
during various stages of Perl-level unwinding no longer needs to take
care to avoid destroying the ghost frame.

=item *

The format of entries on the scope stack has been changed, resulting in a
reduction of memory usage of about 10%. In particular, the memory used by
the scope stack to record each active lexical variable has been halved.

=item *

Memory allocation for pointer tables has been changed. Previously
C<Perl_ptr_table_store> allocated memory from the same arena system as C<SV>
bodies and C<HE>s, with freed memory remaining bound to those arenas until
interpreter exit. Now it allocates memory from arenas private to the specific
pointer table, and that memory is returned to the system when
C<Perl_ptr_table_free> is called. Additionally, allocation and release are both
less CPU intensive.

=item *

A new function, Perl_magic_methcall has been added that wraps the setup needed
to call a magic method like FETCH (the existing S_magic_methcall function has
been renamed S_magic_methcall1).

=item *

The implementation of sv_dup_inc() has changed from a macro to a function.

=item *

The C<find_rundefsvoffset> function has been deprecated. It appeared that
its design was insufficient to reliably get the lexical C<$_> at run-time.

Use the new C<find_rundefsv> function or the C<UNDERBAR> macro instead.
They directly return the right SV representing C<$_>, whether it's lexical
or dynamic (789bd8 .. 03d5bc).

=item *

The following new functions or macros have been added to the public API:
C<SvNV_nomg>,  C<sv_2nv_flags>, C<find_rundefsv>.

=item *

The C<UNDERBAR> macro now calls C<find_rundefsv>. C<dUNDERBAR> is now a
noop but should still be used to ensure past and future compatibility.

=item *

The ibcmp_* functions have been renamed and are now called foldEQ,
foldEQ_locale and foldEQ_utf8 (e6226b).

=item *

Under some circumstances, the C<CvGV()> field of a CV is now reference
counted. To ensure consistent behaviour, direct assignment to it, for
example C<CvGV(cv) = gv> is now a compile-time error. A new macro,
C<CvGV_set(cv,gv)> has been introduced to perform this operation safely.
Note that modification of this field is not part of of the public API,
regardless of this new macro. This change caused some
L<issues|/"Known Problems"> in modules that used the private C<GvGV()>
field.

=item *

It is now possible for XS code to hook into Perl's lexical scope
mechanism at compile time, using the new C<Perl_blockhook_register>
function. See L<perlguts/"Compile-time scope hooks">.

=item *

Added C<Perl_croak_no_modify()> to implement
C<Perl_croak("%s", PL_no_modify)> (6ad8f25)

=item *

Added prototypes for C<tie()> and C<untie()> to allow overloading (RT#75902)
(1db4d19)

=item *

Adds C<my_[l]stat_flags()> to replace C<my_[l]stat()>.  C<my_stat()> and
C<my_lstat()> call get magic on the stack arg, so create C<_flags()>
variants that allow us to control this. (0d7d409)

=item *

Removed C<PERL_POLLUTE>

The option to define C<PERL_POLLUTE> to expose older 5.005 symbols for backwards
compatibility has been removed. It's use was always discouraged, and MakeMaker
contains a more specific escape hatch:

    perl Makefile.PL POLLUTE=1

This can be used for modules that have not been upgraded to 5.6 naming
conventions (and really should be completely obsolete by now).

=item *

Added C<PERL_STATIC_INLINE>

The C<PERL_STATIC_INLINE> define has been added to provide the best-guess
incantation to use for static inline functions, if the C compiler supports
C99-style static inline. If it doesn't, it'll give a plain C<static>.

C<HAS_STATIC_INLINE> can be used to check if the compiler actually supports
inline functions.

=item *

C<CALL_FPTR> and C<CPERLscope> have been deprecated.

Those are left from an old implementation of C<MULTIPLICITY> using C++ objects,
which was removed in Perl 5.8.  Nowadays these macros do exactly nothing, so
they shouldn't be used anymore.

For compatibility, they are still defined for external C<XS> code.  Only
extensions defining C<PERL_CORE> must be updated now.

=item *

C<lex_stuff_pvs()> has been added as a convenience macro wrapping
C<lex_stuff_pvn()> for literal strings.

=item *

The recursive part of the peephole optimizer is now hookable.

In addition to C<PL_peepp>, for hooking into the toplevel peephole optimizer, a
C<PL_rpeepp> is now available to hook into the optimizer recursing into
side-chains of the optree.

=item *

See L</Regular expressions retain their localeness when interpolated>,
above.

=item *

The C<sv_cmp_flags>, C<sv_cmp_locale_flags>, C<sv_eq_flags> and
C<sv_collxfrm_flags> functions have been added. These are like their
non-_flags counterparts, but allow one to specify whether get-magic is
processed.

The C<sv_cmp>, C<sv_cmp_locale>, C<sv_eq> and C<sv_collxfrm> functions have
been replaced with wrappers around the new functions. 

=item *

A new C<sv_2bool_flags> function has been added.

This is like C<sv_2bool>, but it lets the calling code decide whether
get-magic is handled. C<sv_2bool> is now a macro that calls the new
function.

=item *

A new macro, C<SvTRUE_nomg>, has been added.

This is like C<SvTRUE>, except that it does not process magic. It uses the
new C<sv_2bool_flags> function.

=item *

C<sv_catsv_flags> no longer calls C<mg_get> on its second argument (the
source string) if the flags passed to it do not include SV_GMAGIC. So it
now matches the documentation.

=item *

A new interface has been added for custom check hooks on subroutines. See
L</Custom per-subroutine check hooks>, above.

=item *

List op building functions have been added to the
API.  See L<op_append_elem|perlapi/op_append_elem>,
L<op_append_list|perlapi/op_append_list>, and
L<op_prepend_elem|perlapi/op_prepend_elem>.

=item *

The L<LINKLIST|perlapi/LINKLIST> macro, part of op building that
constructs the execution-order op chain, has been added to the API.

=item *

Many functions ending with pvn now have equivalent pv/pvs/sv versions.

=item *

The C<save_freeop>, C<save_op>, C<save_pushi32ptr> and C<save_pushptrptr>
functions have been added to the API.

=item *

The new API function C<parse_stmtseq()> parses a sequence of statements, up
to closing brace or EOF.

=item *

C<lex_start> has been added to the API, but is considered experimental.

=item *

A new C<parse_block> function has been added to the API [perl #78222].

=item *

A new, experimental API has been added for accessing the internal
structure that Perl uses for C<%^H>. See the functions beginning with
C<cophh_> in L<perlapi>.

=item *

A stash can now have a list of effective names in addition to its usual
name. The first effective name can be accessed via the C<HvENAME> macro,
which is now the recommended name to use in MRO linearisations (C<HvNAME>
being a fallback if there is no C<HvENAME>).

These names are added and deleted via C<hv_ename_add> and
C<hv_ename_delete>. These two functions are I<not> part of the API.

=item *

The way the parser handles labels has been cleaned up and refactored. As a
result, the C<newFOROP()> constructor function no longer takes a parameter
stating what label is to go in the state op.

=item *

The C<newWHILEOP()> and C<newFOROP()> functions no longer accept a line
number as a parameter.

=item *

A new C<parse_barestmt()> function has been added, for parsing a statement
without a label.

=item *

A new C<parse_label()> function has been added, that parses a statement
label, separate from statements.

=item *

The C<CvSTASH()> macro can now only be used as an rvalue. C<CvSTASH_set()>
has been added to replace assignment to C<CvSTASH()>. This is to ensure
that backreferences are handled properly. These macros are not part of the
API.

=item *

The C<op_scope()> and C<op_lvalue()> functions have been added to the API,
but are considered experimental.

=item *

The L<C<mg_findext()>|perlapi/mg_findext> and
L<C<sv_unmagicext()>|perlapi/sv_unmagicext>
functions have been added to the API.
They allow extension authors to find and remove magic attached to
scalars based on both the magic type and the magic virtual table, similar to how
C<sv_magicext()> attaches magic of a certain type and with a given virtual table
to a scalar. This eliminates the need for extensions to walk the list of
C<MAGIC> pointers of an C<SV> to find the magic that belongs to them.

=item *

The
L<C<parse_fullexpr()>|perlapi/parse_fullexpr>,
L<C<parse_listexpr()>|perlapi/parse_listexpr>,
L<C<parse_termexpr()>|perlapi/parse_termexpr>, and
L<C<parse_arithexpr()>|perlapi/parse_arithexpr>
functions have been added to the API.  They perform
recursive-descent parsing of expressions at various precedence levels.
They are expected to be used by syntax plugins.

=item *

The opcode bodies for C<chop> and C<chomp> and for C<schop> and C<schomp> have
been merged. The implementation functions C<Perl_do_chop()> and
C<Perl_do_chomp()>, never part of the public API, have been merged and moved to
a static function in F<pp.c>. This shrinks the perl binary slightly, and should
not affect any code outside the core (unless it is relying on the order of side
effects when C<chomp> is passed a I<list> of values).

=item *

Some of the flags parameters to the uvuni_to_utf8_flags() and
utf8n_to_uvuni() have changed.  This is a result of Perl now allowing
internal storage and manipulation of code points that are problematic
in some situations.  Hence, the default actions for these functions has
been complemented to allow these code points.  The new flags are
documented in L<perlapi>.  Code that requires the problematic code
points to be rejected needs to change to use these flags.  Some flag
names are retained for backward source compatibility, though they do
nothing, as they are now the default.  However the flags
C<UNICODE_ALLOW_FDD0>, C<UNICODE_ALLOW_FFFF>, C<UNICODE_ILLEGAL>, and
C<UNICODE_IS_ILLEGAL> have been removed, as they stem from a
fundamentally broken model of how the Unicode non-character code points
should be handled, which is now described in
L<perlunicode/Non-character code points>.  See also L</Selected Bug Fixes>.

=item *

Certain shared flags in the C<pmop.op_pmflags> and C<regexp.extflags>
structures have been removed.  These are: C<Rxf_Pmf_LOCALE>,
C<Rxf_Pmf_UNICODE>, and C<PMf_LOCALE>.  Instead there are encodes and
three static in-line functions for accessing the information:
C<get_regex_charset()>, C<set_regex_charset()>, and C<get_regex_charset_name()>,
which are defined in the places where the original flags were.

=item *

A new option has been added to C<pv_escape> to dump all characters above
ASCII in hexadecimal. Before, one could get all characters as hexadecimal
or the Latin1 non-ASCII as octal


=item *

Generate pp_* prototypes in pp_proto.h, and remove pp.sym

Eliminate the #define pp_foo Perl_pp_foo(pTHX) macros, and update the 13
locations that relied on them.

regen/opcode.pl now generates prototypes for the PP functions directly, into
pp_proto.h. It no longer writes pp.sym, and regen/embed.pl no longer reads
this, removing the only ordering dependency in the regen scripts. opcode.pl
is now responsible for prototypes for pp_* functions. (embed.pl remains
responsible for ck_* functions, reading from regen/opcodes)

=item *

Fix harmless invalid read in Perl_re_compile() (f6d9469)

[perl #2460] described a case where electric fence reported an invalid
read. This could be reproduced under valgrind with blead and -e'/x/',
but only on a non-debugging build.

This was because it was checking for certain pairs of nodes (e.g. BOL + END)
and wasn't allowing for EXACT nodes, which have the string at the next
node position when using a naive NEXTOPER(first). In the non-debugging
build, the nodes aren't initialised to zero, and a 1-char EXACT node isn't
long enough to spill into the type field of the "next node".

Fix this by only using NEXTOPER(first) when we know the first node is
kosher.

=item *

Break out the generated function Perl_keywords() into F<keywords.c>, a new file. (26ea9e1)

As it and Perl_yylex() both need FEATURE_IS_ENABLED, feature_is_enabled() is
no longer static, and the two macro definitions move from toke.c to perl.h

Previously, one had to cut and paste the output of perl_keywords.pl into the
middle of toke.c, and it was not clear that it was generated code.

=item *

A lot of tests have been ported from Test to Test::More, e.g. in
3842ad6.

=item *

Increase default PerlIO buffer size. (b83080d)

The previous default size of a PerlIO buffer (4096 bytes) has been increased
to the larger of 8192 bytes and your local BUFSIZ.  Benchmarks show that doubling
this decade-old default increases read and write performance in the neighborhood
of 25% to 50% when using the default layers of perlio on top of unix.  To choose
a non-default size, such as to get back the old value or to obtain and even
larger value, configure with:

     ./Configure -Accflags=-DPERLIOBUF_DEFAULT_BUFSIZ=N

where N is the desired size in bytes; it should probably be a multiple of
your page size.

=back

=head1 Selected Bug Fixes

=over 4

=item *

C<when(scalar){...}> no longer crashes, but produces a syntax error
[perl #74114].

=item *

The C-level C<lex_stuff_pvn> function would sometimes cause a spurious
syntax error on the last line of the file if it lacked a final semicolon
[perl #74006].

=item *

The regular expression engine no longer loops when matching
C<"\N{LATIN SMALL LIGATURE FF}" =~ /f+/i> and similar expressions
[perl #72998].

=item *

A label right before a string eval (C<foo: eval $string>) no longer causes
the label to be associated also with the first statement inside the eval
[perl #74290] (5.12.1).

=item *

Naming a deprecated character in \N{...} will not leak memory.

=item *

FETCH is no longer called needlessly on some tied variables.

=item *

The trie runtime code should no longer allocate massive amounts of memory,
fixing #74484.

=item *

Timely cleanup of SVs that are cloned into a new thread but then
discovered to be orphaned (i.e. their owners are -not- cloned) (e42956)

=item *

Don't accidentally clone lexicals in scope within active stack frames in
the parent when creating a child thread (RT #73086) (05d04d).

=item *

Avoid loading feature.pm when 'no 5.13.2;' or similar is
encountered (faee19).

=item *

Trap invalid use of SvIVX on SVt_REGEXP when assertions are on
(e77da3)

=item *

Don't stamp on $DB::single, $DB::trace and $DB::signal if they
already have values when $^P is assigned to (RT #72422) (4c0f30).

=item *

chop now correctly handles perl's extended UTF-8 (RT #73246) (65ab92)

=item *

Defer signal handling when shared SV locks are held to avoid
deadlocks (RT #74868) (65c742).

=item *

glob() no longer crashes when %File::Glob:: is empty and
CORE::GLOBAL::glob isn't present (4984aa).

=item *

perlbug now always permits the sender address to be changed
before sending - if you were having trouble sending bug reports before
now, this should fix it, we hope (e6eb90).

=item *

Overloading now works properly in conjunction with tied
variables. What formerly happened was that most ops checked their
arguments for overloading I<before> checking for magic, so for example
an overloaded object returned by a tied array access would usually be
treated as not overloaded (RT #57012) (6f1401, ed3b9b, 6a5f8c .. 24328f).

=item *

Independently, a bug was fixed that prevented $tied-E<gt>() from
always calling FETCH correctly (RT #8438) (7c7501)

=item *

Some work has been done on the internal pointers that link between symbol
tables (stashes), typeglobs and subroutines. This has the effect that
various edge cases related to deleting stashes or stash entries (e.g.
<%FOO:: = ()>), and complex typeglob or code reference aliasing, will no
longer crash the interpreter.

=item *

Fixed readline() when interrupted by signals so it no longer returns
the "same thing" as before or random memory

=item *

Fixed a regression of kill() when a match variable is used for the
process ID to kill  (RT#75812) (8af710e)

=item *

Fixed several subtle bugs in sort() when @_ is accessed within a subroutine
used for sorting (RT#72334) (8f443ca)

=item *

Catch yyparse() exceptions in C<< (?{...}) >> (RT#2353) (634d691)

=item *

Avoid UTF-8 cache panics with offsets beyond a string (RT #75898) (3e2d381)

=item *

Fixed POSIX::strftime memory leak (RT#73520) (c4bc4aa)

=item *

Doesn't set strict with C<no VERSION> if C<VERSION> is greater than 5.12
(da8fb5d)

=item *

Avoids multiple FETCH/stringify on filetest ops (40c852d)

=item *

Fixed issue with string C<eval> not detecting taint of overloaded/tied
arguments (RT #75716) (895b760)

=item *

Fix potential crashes of string C<eval> when evaluating a object with
overloaded stringification by creating a stringified copy when necessary
(3e5c018)

=item *

Fixed bug where overloaded stringification could remove tainting
(RT #75716) (a02ec77)

=item *

Plugs more memory leaks in vms.c. (9e2bec0)

=item *

Fix pthread include error for Time::Piece (e9f284c)

=item *

A possible memory leak when using L<caller()|perlfunc/"caller EXPR"> to set
C<@DB::args> has been fixed.

=item *

Several memory leaks when loading XS modules were fixed.

=item *

A panic in the regular expression optimizer has been fixed (RT#75762).

=item *

Assignments to lvalue subroutines now honor copy-on-write behavior again, which
has been broken since version 5.10.0 (RT#75656).

=item *

Assignments to glob copies now behave just like assignments to regular globs
(RT#1804).

=item *

Within signal handlers, C<$!> is now implicitly localized.

=item *

L<readline|perlfunc/"readline EXPR"> now honors C<< <> >> overloading on tied
arguments.

=item *

L<substr()|perlfunc/"substr EXPR,OFFSET,LENGTH,REPLACEMENT">,
L<pos()|perlfunc/"index STR,SUBSTR,POSITION">, L<keys()|perlfunc/"keys HASH">,
and L<vec()|perlfunc/"vec EXPR,OFFSET,BITS"> could, when used in combination
with lvalues, result in leaking the scalar value they operate on, and cause its
destruction to happen too late. This has now been fixed.

=item *

Building with C<PERL_GLOBAL_STRUCT>, which has been broken accidentally in
5.13.3, now works again.

=item *

A regression introduced in Perl 5.12.0, making
C<< my $x = 3; $x = length(undef) >> result in C<$x> set to C<3> has been
fixed.  C<$x> will now be C<undef>.

=item *

A fatal error in regular expressions when processing UTF-8 data has been fixed [perl #75680].

=item *

An erroneous regular expression engine optimization that caused regex verbs like
C<*COMMIT> to sometimes be ignored has been removed.

=item *

The Perl debugger now also works in taint mode [perl #76872].

=item *

Several memory leaks in cloning and freeing threaded Perl interpreters have been
fixed [perl #77352].

=item *

A possible string corruption when doing regular expression matches on overloaded
objects has been fixed [perl #77084].

=item *

Magic applied to variables in the main package no longer affects other packages.
See L</Magic variables outside the main package> above [perl #76138].

=item *

Opening a glob reference via C<< open $fh, "E<gt>", \*glob >> will no longer
cause the glob to be corrupted when the filehandle is printed to.  This would
cause perl to crash whenever the glob's contents were accessed
[perl #77492].

=item *

The postincrement and postdecrement operators, C<++> and C<-->, used to cause
leaks when being used on references.  This has now been fixed.

=item *

A bug when replacing the glob of a loop variable within the loop has been fixed
[perl #21469].  This
means the following code will no longer crash:

    for $x (...) {
        *x = *y;
    }

=item *

Perl would segfault if the undocumented C<Internals> functions that used
reference prototypes were called with the C<&foo()> syntax, e.g.
C<&Internals::SvREADONLY(undef)> [perl #77776].

These functions now call C<SvROK> on their arguments before dereferencing them
with C<SvRV>, and we test for this case in F<t/lib/universal.t>.

=item *

When assigning a list with duplicated keys to a hash, the assignment used to
return garbage and/or freed values:

    @a = %h = (list with some duplicate keys);

This has now been fixed [perl #31865].

=item *

An earlier release of the 5.13 series of Perl changed the semantics of opening a
reference to a copy of a glob:

    my $var = *STDOUT;
    open my $fh, '>', \$var;

This was a mistake, and the previous behaviour from Perl 5.10 and 5.12, which is
to treat \$var as a scalar reference, has now been restored.

=item *

The regular expression bracketed character class C<[\8\9]> was effectively the
same as C<[89\000]>, incorrectly matching a NULL character.  It also gave
incorrect warnings that the C<8> and C<9> were ignored.  Now C<[\8\9]> is the
same as C<[89]> and gives legitimate warnings that C<\8> and C<\9> are
unrecognized escape sequences, passed-through.

=item *

C<warn()> and C<die()> now respect utf8-encoded scalars [perl #45549].

=item *

A regular expression match in the right-hand side of a global substitution
(C<s///g>) that is in the same scope will no longer cause match variables
to have the wrong values on subsequent iterations. This can happen when an
array or hash subscript is interpolated in the right-hand side, as in
C<s|(.)|@a{ print($1), /./ }|g> [perl #19078].

=item *

Constant-folding used to cause

  $text =~ ( 1 ? /phoo/ : /bear/)

to turn into

  $text =~ /phoo/

at compile time. Now it correctly matches against C<$_> [perl #20444].

=item *

Parsing Perl code (either with string C<eval> or by loading modules) from
within a C<UNITCHECK> block no longer causes the interpreter to crash
[perl #70614].

=item *

When C<-d> is used on the shebang (C<#!>) line, the debugger now has access
to the lines of the main program. In the past, this sometimes worked and
sometimes did not, depending on what order things happened to be arranged
in memory [perl #71806].

=item *

The C<y///> or C<tr///> operator now calls get-magic (e.g., the C<FETCH>
method of a tie) on its left-hand side just once, not twice [perl #76814].

=item *

String comparison (C<eq>, C<ne>, C<lt>, C<gt>, C<le>, C<ge> and
C<cmp>) and logical not (C<not> and C<!>) operators no longer call magic
(e.g., tie methods) twice on their operands [perl #76814].

This bug was introduced in an earlier 5.13 release, and does not affect
perl 5.12.

=item *

When a tied (or other magic) variable is used as, or in, a regular
expression, it no longer has its C<FETCH> method called twice
[perl #76814].

This bug was introduced in an earlier 5.13 release, and does not affect
perl 5.12.

=item *

The C<-C> command line option can now be followed by other options
[perl #72434].

=item *

Assigning a glob to a PVLV used to convert it to a plain string. Now it
works correctly, and a PVLV can hold a glob. This would happen when a
nonexistent hash or array element was passed to a subroutine:

  sub { $_[0] = *foo }->($hash{key});
  # $_[0] would have been the string "*main::foo"

It also happened when a glob was assigned to, or returned from, an element
of a tied array or hash [perl #36051].

=item *

Creating a new thread when directory handles were open used to cause a
crash, because the handles were not cloned, but simply passed to the new
thread, resulting in a double free.

Now directory handles are cloned properly, on systems that have a C<fchdir>
function. On other systems, new threads simply do not inherit directory
handles from their parent threads [perl #75154].

=item *

The regular expression parser no longer hangs when parsing C<\18> and
C<\88>.

This bug was introduced in version 5.13.5 and did not affect earlier
versions [perl #78058].

=item *

Subroutine redefinition works once more in the debugger [perl #48332].

=item *

The C<&> C<|> C<^> bitwise operators no longer coerce read-only arguments
[perl #20661].

=item *

Stringifying a scalar containing -0.0 no longer has the affect of turning
false into true [perl #45133].

=item *

Aliasing packages by assigning to globs or deleting packages by deleting
their containing stash elements used to have erratic effects on method
resolution, because the internal 'isa' caches were not reset. This has been
fixed.

=item *

C<sort> with a custom sort routine could crash if too many nested
subroutine calls occurred from within the sort routine [perl #77930].

This bug was introduced in an earlier 5.13 release, and did not affect
perl 5.12.

=item *

The C<eval_sv> and C<eval_pv> C functions now set C<$@> correctly when
there is a syntax error and no C<G_KEEPERR> flag, and never set it if the
C<G_KEEPERR> flag is present [perl #3719].

=item *

Nested C<map> and C<grep> blocks no longer leak memory when processing
large lists [perl #48004].

=item *

Malformed C<version> objects no longer cause crashes [perl #78286].

=item *

The interpreter no longer crashes when freeing deeply-nested arrays of
arrays. Hashes have not been fixed yet [perl #44225].

=item *

The mechanism for freeing objects in globs used to leave dangling
pointers to freed SVs, meaning Perl users could see corrupted state
during destruction.

Perl now only frees the affected slots of the GV, rather than freeing
the GV itself. This makes sure that there are no dangling refs or
corrupted state during destruction.

=item *

The typeglob C<*,>, which holds the scalar variable C<$,> (output field
separator), had the wrong reference count in child threads.

=item *

C<splice> now calls set-magic. This means that, for instance, changes made
by C<splice @ISA> are respected by method calls [perl #78400].

=item *

C<use v5.8> no longer leaks memory [perl #78436].

=item *

The XS multicall API no longer causes subroutines to lose reference counts
if called via the multicall interface from within those very subroutines.
This affects modules like List::Util. Calling one of its functions with an
active subroutine as the first argument could cause a crash [perl #78070].

=item *

The C<parse_stmt> C function added in earlier in the 5.13.x series has been
fixed to work with statements ending with C<}> [perl #78222].

=item *

The C<parse_fullstmt> C function added in 5.13.5 has been fixed to work
when called while an expression is being parsed.

=item *

Characters in the Latin-1 non-ASCII range (0x80 to 0xFF) used not to match
themselves if the string happened to be UTF8-encoded internally, the
regular expression was not, and the character in the regular expression was
inside a repeated group (e.g.,
C<Encode::decode_utf8("\303\200") =~ /(\xc0)+/>) [perl #78464].

=item *

The C<(?d)> regular expression construct now overrides a previous C<(?u)>
or C<use feature "unicode_string"> [perl #78508].

=item *

A memory leak in C<do "file">, introduced in perl 5.13.6, has been fixed
[perl #78488].

=item *

Various bugs related to typeglob dereferencing have been fixed. See
L</Dereferencing typeglobs>, above.

=item *

The C<SvPVbyte> function available to XS modules now calls magic before
downgrading the SV, to avoid warnings about wide characters [perl #72398].

=item *

The C<=> operator used to ignore magic (e.g., tie methods) on its
right-hand side if the scalar happened to hold a typeglob. This could
happen if a typeglob was the last thing returned from or assigned to a tied
scalar [perl #77498].

=item *

C<sprintf> was ignoring locales when called with constant arguments
[perl #78632].

=item *

A non-ASCII character in the Latin-1 range could match both a Posix
class, such as C<[[:alnum:]]>, and its inverse C<[[:^alnum:]]>.  This is
now fixed for regular expressions compiled under the C<"u"> modifier.
See L</C<use feature "unicode_strings"> now applies to more regex matching>. [perl #18281].

=item *

Concatenating long strings under C<use encoding> no longer causes perl to
crash [perl #78674].

=item *

Typeglob assignments would crash if the glob's stash no longer existed, so
long as the glob assigned to was named 'ISA' or the glob on either side of
the assignment contained a subroutine.

=item *

Calling C<< ->import >> on a class lacking an import method could corrupt
the stack, resulting in strange behaviour. For instance,

  push @a, "foo", $b = bar->import;

would assign 'foo' to C<$b> [perl #63790].

=item *

Creating an alias to a package when that package had been detached from the
symbol table would result in corrupted isa caches [perl #77358].

=item *

C<.=> followed by C<< <> >> or C<readline> would leak memory if C<$/>
contained characters beyond the octet range and the scalar assigned to
happened to be encoded as UTF8 internally [perl #72246].

=item *

The C<recv> function could crash when called with the MSG_TRUNC flag
[perl #75082].