-Drv now turns on all regex debugging

[perl5.git] / pod / perl5120delta.pod

diff --git a/pod/perl5120delta.pod b/pod/perl5120delta.pod
index 922aa97..5b5eac0 100644 (file)
--- a/pod/perl5120delta.pod
+++ b/pod/perl5120delta.pod
@@ -1,16 +1,3195 @@
+=encoding utf8
+
 =head1 NAME
 
 perl5120delta - what is new for perl v5.12.0
 
 =head1 DESCRIPTION
 
-This document describes differences between the 5.10.0 release and
-the 5.12.0 release.
+This document describes differences between the 5.10.0 release and the
+5.12.0 release.
+
+Many of the bug fixes in 5.12.0 are already included in the 5.10.1
+maintenance release.
+
+You can see the list of those changes in the 5.10.1 release notes
+(L<perl5101delta>).
+
+
+=head1 Core Enhancements
+
+=head2 New C<package NAME VERSION> syntax
+
+This new syntax allows a module author to set the $VERSION of a namespace
+when the namespace is declared with 'package'. It eliminates the need
+for C<our $VERSION = ...> and similar constructs. E.g.
+
+      package Foo::Bar 1.23;
+      # $Foo::Bar::VERSION == 1.23
+
+There are several advantages to this:
+
+=over
+
+=item *
+
+C<$VERSION> is parsed in exactly the same way as C<use NAME VERSION>
+
+=item *
+
+C<$VERSION> is set at compile time
+
+=item *
+
+C<$VERSION> is a version object that provides proper overloading of
+comparison operators so comparing C<$VERSION> to decimal (1.23) or
+dotted-decimal (v1.2.3) version numbers works correctly.
+
+=item *
+
+Eliminates C<$VERSION = ...> and C<eval $VERSION> clutter
+
+=item *
+
+As it requires VERSION to be a numeric literal or v-string
+literal, it can be statically parsed by toolchain modules
+without C<eval> the way MM-E<gt>parse_version does for C<$VERSION = ...>
+
+=back
+
+It does not break old code with only C<package NAME>, but code that uses
+C<package NAME VERSION> will need to be restricted to perl 5.12.0 or newer
+This is analogous to the change to C<open> from two-args to three-args.
+Users requiring the latest Perl will benefit, and perhaps after several
+years, it will become a standard practice.
+
+
+However, C<package NAME VERSION> requires a new, 'strict' version
+number format. See L</"Version number formats"> for details.
+
+
+=head2 The C<...> operator
+
+A new operator, C<...>, nicknamed the Yada Yada operator, has been added.
+It is intended to mark placeholder code that is not yet implemented.
+See L<perlop/"Yada Yada Operator">.
+
+=head2 Implicit strictures
+
+Using the C<use VERSION> syntax with a version number greater or equal
+to 5.11.0 will lexically enable strictures just like C<use strict>
+would do (in addition to enabling features.) The following:
+
+    use 5.12.0;
+
+means:
+
+    use strict;
+    use feature ':5.12';
+
+=head2 Unicode improvements
+
+Perl 5.12 comes with Unicode 5.2, the latest version available to
+us at the time of release.  This version of Unicode was released in
+October 2009. See L<http://www.unicode.org/versions/Unicode5.2.0> for
+further details about what's changed in this version of the standard.
+See L<perlunicode> for instructions on installing and using other versions
+of Unicode.
+
+Additionally, Perl's developers have significantly improved Perl's Unicode
+implementation. For full details, see L</Unicode overhaul> below.
+
+=head2 Y2038 compliance
+
+Perl's core time-related functions are now Y2038 compliant. (It may not mean much to you, but your kids will love it!)
+
+=head2 qr overloading
+
+It is now possible to overload the C<qr//> operator, that is,
+conversion to regexp, like it was already possible to overload
+conversion to boolean, string or number of objects. It is invoked when
+an object appears on the right hand side of the C<=~> operator or when
+it is interpolated into a regexp. See L<overload>.
+
+=head2 Pluggable keywords
+
+Extension modules can now cleanly hook into the Perl parser to define
+new kinds of keyword-headed expression and compound statement. The
+syntax following the keyword is defined entirely by the extension. This
+allows a completely non-Perl sublanguage to be parsed inline, with the
+correct ops cleanly generated.
+
+See L<perlapi/PL_keyword_plugin> for the mechanism. The Perl core
+source distribution also includes a new module
+L<XS::APItest::KeywordRPN>, which implements reverse Polish notation
+arithmetic via pluggable keywords. This module is mainly used for test
+purposes, and is not normally installed, but also serves as an example
+of how to use the new mechanism.
+
+Perl's developers consider this feature to be experimental. We may remove
+it or change it in a backwards-incompatible way in Perl 5.14.
+
+=head2 APIs for more internals
+
+The lowest layers of the lexer and parts of the pad system now have C
+APIs available to XS extensions. These are necessary to support proper
+use of pluggable keywords, but have other uses too. The new APIs are
+experimental, and only cover a small proportion of what would be
+necessary to take full advantage of the core's facilities in these
+areas. It is intended that the Perl 5.13 development cycle will see the
+addition of a full range of clean, supported interfaces.
+
+Perl's developers consider this feature to be experimental. We may remove
+it or change it in a backwards-incompatible way in Perl 5.14.
+
+=head2 Overridable function lookup
+
+Where an extension module hooks the creation of rv2cv ops to modify the
+subroutine lookup process, this now works correctly for bareword
+subroutine calls. This means that prototypes on subroutines referenced
+this way will be processed correctly. (Previously bareword subroutine
+names were initially looked up, for parsing purposes, by an unhookable
+mechanism, so extensions could only properly influence subroutine names
+that appeared with an C<&> sigil.)
+
+=head2 A proper interface for pluggable Method Resolution Orders
+
+As of Perl 5.12.0 there is a new interface for plugging and using method
+resolution orders other than the default linear depth first search.
+The C3 method resolution order added in 5.10.0 has been re-implemented as
+a plugin, without changing its Perl-space interface. See L<perlmroapi> for
+more information.
+
+
+
+=head2 C<\N> experimental regex escape
+
+Perl now supports C<\N>, a new regex escape which you can think of as
+the inverse of C<\n>. It will match any character that is not a newline,
+independently from the presence or absence of the single line match
+modifier C</s>. It is not usable within a character class.  C<\N{3}>
+means to match 3 non-newlines; C<\N{5,}> means to match at least 5.
+C<\N{NAME}> still means the character or sequence named C<NAME>, but
+C<NAME> no longer can be things like C<3>, or C<5,>.
+
+This will break a L<custom charnames translator|charnames/CUSTOM
+TRANSLATORS> which allows numbers for character names, as C<\N{3}> will
+now mean to match 3 non-newline characters, and not the character whose
+name is C<3>. (No name defined by the Unicode standard is a number,
+so only custom translators might be affected.)
+
+Perl's developers are somewhat concerned about possible user confusion
+with the existing C<\N{...}> construct which matches characters by their
+Unicode name. Consequently, this feature is experimental. We may remove
+it or change it in a backwards-incompatible way in Perl 5.14.
+
+=head2 DTrace support
+
+Perl now has some support for DTrace. See "DTrace support" in F<INSTALL>.
+
+=head2 Support for C<configure_requires> in CPAN module metadata
+
+Both C<CPAN> and C<CPANPLUS> now support the C<configure_requires>
+keyword in the F<META.yml> metadata file included in most recent CPAN
+distributions.  This allows distribution authors to specify configuration
+prerequisites that must be installed before running F<Makefile.PL>
+or F<Build.PL>.
+
+See the documentation for C<ExtUtils::MakeMaker> or C<Module::Build> for
+more on how to specify C<configure_requires> when creating a distribution
+for CPAN.
+
+=head2 C<each>, C<keys>, C<values> are now more flexible
+
+The C<each>, C<keys>, C<values> function can now operate on arrays.
+
+=head2 C<when> as a statement modifier
+
+C<when> is now allowed to be used as a statement modifier.
+
+=head2 C<$,> flexibility
+
+The variable C<$,> may now be tied.
+
+=head2 // in when clauses
+
+// now behaves like || in when clauses
+
+=head2 Enabling warnings from your shell environment
+
+You can now set C<-W> from the C<PERL5OPT> environment variable
+
+=head2 C<delete local>
+
+C<delete local> now allows you to locally delete a hash entry.
+
+=head2 New support for Abstract namespace sockets
+
+Abstract namespace sockets are Linux-specific socket type that live in
+AF_UNIX family, slightly abusing it to be able to use arbitrary
+character arrays as addresses: They start with nul byte and are not
+terminated by nul byte, but with the length passed to the socket()
+system call.
+
+=head2 32-bit limit on substr arguments removed
+
+The 32-bit limit on C<substr> arguments has now been removed. The full
+range of the system's signed and unsigned integers is now available for
+the C<pos> and C<len> arguments.
+
+=head1 Potentially Incompatible Changes
+
+=head2 Deprecations warn by default
+
+Over the years, Perl's developers have deprecated a number of language
+features for a variety of reasons.  Perl now defaults to issuing a
+warning if a deprecated language feature is used. Many of the deprecations
+Perl now warns you about have been deprecated for many years.  You can
+find a list of what was deprecated in a given release of Perl in the
+C<perl5xxdelta.pod> file for that release.
+
+To disable this feature in a given lexical scope, you should use C<no
+warnings 'deprecated';> For information about which language features
+are deprecated and explanations of various deprecation warnings, please
+see L<perldiag>. See L</Deprecations> below for the list of features
+and modules Perl's developers have deprecated as part of this release.
+
+=head2 Version number formats
+
+Acceptable version number formats have been formalized into "strict" and
+"lax" rules. C<package NAME VERSION> takes a strict version number.
+C<UNIVERSAL::VERSION> and the L<version> object constructors take lax
+version numbers. Providing an invalid version will result in a fatal
+error. The version argument in C<use NAME VERSION> is first parsed as a
+numeric literal or v-string and then passed to C<UNIVERSAL::VERSION>
+(and must then pass the "lax" format test).
+
+These formats are documented fully in the L<version> module. To a first
+approximation, a "strict" version number is a positive decimal number
+(integer or decimal-fraction) without exponentiation or else a
+dotted-decimal v-string with a leading 'v' character and at least three
+components. A "lax" version number allows v-strings with fewer than
+three components or without a leading 'v'. Under "lax" rules, both
+decimal and dotted-decimal versions may have a trailing "alpha"
+component separated by an underscore character after a fractional or
+dotted-decimal component.
+
+The L<version> module adds C<version::is_strict> and C<version::is_lax>
+functions to check a scalar against these rules.
+
+=head2 @INC reorganization
+
+In C<@INC>, C<ARCHLIB> and C<PRIVLIB> now occur after the current
+version's C<site_perl> and C<vendor_perl>.  Modules installed into
+C<site_perl> and C<vendor_perl> will now be loaded in preference to
+those installed in C<ARCHLIB> and C<PRIVLIB>.
+
+
+=head2 REGEXPs are now first class
+
+Internally, Perl now treats compiled regular expressions (such as
+those created with C<qr//>) as first class entities. Perl modules which
+serialize, deserialize or otherwise have deep interaction with Perl's
+internal data structures need to be updated for this change.  Most
+affected CPAN modules have already been updated as of this writing.
+
+=head2 Switch statement changes
+
+The C<given>/C<when> switch statement handles complex statements better
+than Perl 5.10.0 did (These enhancements are also available in
+5.10.1 and subsequent 5.10 releases.) There are two new cases where
+C<when> now interprets its argument as a boolean, instead of an
+expression to be used in a smart match:
+
+=over
+
+=item flip-flop operators
+
+The C<..> and C<...> flip-flop operators are now evaluated in boolean
+context, following their usual semantics; see L<perlop/"Range Operators">.
+
+Note that, as in perl 5.10.0, C<when (1..10)> will not work to test
+whether a given value is an integer between 1 and 10; you should use
+C<when ([1..10])> instead (note the array reference).
+
+However, contrary to 5.10.0, evaluating the flip-flop operators in
+boolean context ensures it can now be useful in a C<when()>, notably
+for implementing bistable conditions, like in:
+
+    when (/^=begin/ .. /^=end/) {
+      # do something
+    }
+
+=item defined-or operator
+
+A compound expression involving the defined-or operator, as in
+C<when (expr1 // expr2)>, will be treated as boolean if the first
+expression is boolean. (This just extends the existing rule that applies
+to the regular or operator, as in C<when (expr1 || expr2)>.)
+
+=back
+
+=head2 Smart match changes
+
+Since Perl 5.10.0, Perl's developers have made a number of changes to
+the smart match operator. These, of course, also alter the behaviour
+of the switch statements where smart matching is implicitly used.
+These changes were also made for the 5.10.1 release, and will remain in
+subsequent 5.10 releases.
+
+=head3 Changes to type-based dispatch
+
+The smart match operator C<~~> is no longer commutative. The behaviour of
+a smart match now depends primarily on the type of its right hand
+argument. Moreover, its semantics have been adjusted for greater
+consistency or usefulness in several cases. While the general backwards
+compatibility is maintained, several changes must be noted:
+
+=over 4
+
+=item *
+
+Code references with an empty prototype are no longer treated specially.
+They are passed an argument like the other code references (even if they
+choose to ignore it).
+
+=item *
+
+C<%hash ~~ sub {}> and C<@array ~~ sub {}> now test that the subroutine
+returns a true value for each key of the hash (or element of the
+array), instead of passing the whole hash or array as a reference to
+the subroutine.
+
+=item *
+
+Due to the commutativity breakage, code references are no longer
+treated specially when appearing on the left of the C<~~> operator,
+but like any vulgar scalar.
+
+=item *
+
+C<undef ~~ %hash> is always false (since C<undef> can't be a key in a
+hash). No implicit conversion to C<""> is done (as was the case in perl
+5.10.0).
+
+=item *
+
+C<$scalar ~~ @array> now always distributes the smart match across the
+elements of the array. It's true if one element in @array verifies
+C<$scalar ~~ $element>. This is a generalization of the old behaviour
+that tested whether the array contained the scalar.
+
+=back
+
+The full dispatch table for the smart match operator is given in
+L<perlsyn/"Smart matching in detail">.
+
+=head3 Smart match and overloading
+
+According to the rule of dispatch based on the rightmost argument type,
+when an object overloading C<~~> appears on the right side of the
+operator, the overload routine will always be called (with a 3rd argument
+set to a true value, see L<overload>.) However, when the object will
+appear on the left, the overload routine will be called only when the
+rightmost argument is a simple scalar. This way, distributivity of smart
+match across arrays is not broken, as well as the other behaviours with
+complex types (coderefs, hashes, regexes). Thus, writers of overloading
+routines for smart match mostly need to worry only with comparing
+against a scalar, and possibly with stringification overloading; the
+other common cases will be automatically handled consistently.
+
+C<~~> will now refuse to work on objects that do not overload it (in order
+to avoid relying on the object's underlying structure). (However, if the
+object overloads the stringification or the numification operators, and
+if overload fallback is active, it will be used instead, as usual.)
+
+=head2 Other potentially incompatible changes
+
+=over 4
+
+=item *
+
+The definitions of a number of Unicode properties have changed to match
+those of the current Unicode standard. These are listed above under
+L</Unicode overhaul>. This change may break code that expects the old
+definitions.
+
+=item *
+
+The boolkeys op has moved to the group of hash ops. This breaks binary
+compatibility.
+
+=item *
+
+Filehandles are now always blessed into C<IO::File>.
+
+The previous behaviour was to bless Filehandles into L<FileHandle>
+(an empty proxy class) if it was loaded into memory and otherwise
+to bless them into C<IO::Handle>.
+
+=item *
+
+The semantics of C<use feature :5.10*> have changed slightly.
+See L</"Modules and Pragmata"> for more information.
+
+=item *
+
+Perl's developers now use git, rather than Perforce.  This should be
+a purely internal change only relevant to people actively working on
+the core.  However, you may see minor difference in perl as a consequence
+of the change.  For example in some of details of the output of C<perl
+-V>. See L<perlrepository> for more information.
+
+=item *
+
+As part of the C<Test::Harness> 2.x to 3.x upgrade, the experimental
+C<Test::Harness::Straps> module has been removed.
+See L</"Modules and Pragmata"> for more details.
+
+=item *
+
+As part of the C<ExtUtils::MakeMaker> upgrade, the
+C<ExtUtils::MakeMaker::bytes> and C<ExtUtils::MakeMaker::vmsish> modules
+have been removed from this distribution.
+
+=item *
+
+C<Module::CoreList> no longer contains the C<%:patchlevel> hash.
+
+=item *
+
+C<length undef> now returns undef.
+
+=item *
+
+Unsupported private C API functions are now declared "static" to prevent
+leakage to Perl's public API.
+
+=item *
+
+To support the bootstrapping process, F<miniperl> no longer builds with
+UTF-8 support in the regexp engine.
+
+This allows a build to complete with PERL_UNICODE set and a UTF-8 locale.
+Without this there's a bootstrapping problem, as miniperl can't load
+the UTF-8 components of the regexp engine, because they're not yet built.
+
+=item *
+
+F<miniperl>'s @INC is now restricted to just C<-I...>, the split of
+C<$ENV{PERL5LIB}>, and "C<.>"
+
+=item *
+
+A space or a newline is now required after a C<"#line XXX"> directive.
+
+=item *
+
+Tied filehandles now have an additional method EOF which provides the
+EOF type.
+
+=item *
+
+To better match all other flow control statements, C<foreach> may no
+longer be used as an attribute.
+
+=item *
+
+Perl's command-line switch "-P", which was deprecated in version 5.10.0, has
+now been removed. The CPAN module C<< Filter::cpp >> can be used as an 
+alternative.
+
+=back
+
+
+=head1 Deprecations
+
+From time to time, Perl's developers find it necessary to deprecate
+features or modules we've previously shipped as part of the core
+distribution. We are well aware of the pain and frustration that a
+backwards-incompatible change to Perl can cause for developers building
+or maintaining software in Perl. You can be sure that when we deprecate
+a functionality or syntax, it isn't a choice we make lightly. Sometimes,
+we choose to deprecate functionality or syntax because it was found to
+be poorly designed or implemented. Sometimes, this is because they're
+holding back other features or causing performance problems. Sometimes,
+the reasons are more complex. Wherever possible, we try to keep deprecated
+functionality available to developers in its previous form for at least
+one major release. So long as a deprecated feature isn't actively
+disrupting our ability to maintain and extend Perl, we'll try to leave
+it in place as long as possible.
+
+The following items are now deprecated:
+
+=over
+
+=item suidperl
+
+C<suidperl> is no longer part of Perl. It used to provide a mechanism to
+emulate setuid permission bits on systems that don't support it properly.
+
+=item Use of C<:=> to mean an empty attribute list
+
+An accident of Perl's parser meant that these constructions were all
+equivalent:
+
+    my $pi := 4;
+    my $pi : = 4;
+    my $pi :  = 4;
+
+with the C<:> being treated as the start of an attribute list, which
+ends before the C<=>. As whitespace is not significant here, all are
+parsed as an empty attribute list, hence all the above are equivalent
+to, and better written as
+
+    my $pi = 4;
+
+because no attribute processing is done for an empty list.
+
+As is, this meant that C<:=> cannot be used as a new token, without
+silently changing the meaning of existing code. Hence that particular
+form is now deprecated, and will become a syntax error. If it is
+absolutely necessary to have empty attribute lists (for example,
+because of a code generator) then avoid the warning by adding a space
+before the C<=>.
+
+=item C<< UNIVERSAL->import() >>
+
+The method C<< UNIVERSAL->import() >> is now deprecated. Attempting to
+pass import arguments to a C<use UNIVERSAL> statement will result in a
+deprecation warning.
+
+=item Use of "goto" to jump into a construct
+
+Using C<goto> to jump from an outer scope into an inner scope is now
+deprecated. This rare use case was causing problems in the
+implementation of scopes.
+
+=item Custom character names in \N{name} that don't look like names
+
+In C<\N{I<name>}>, I<name> can be just about anything. The standard
+Unicode names have a very limited domain, but a custom name translator
+could create names that are, for example, made up entirely of punctuation
+symbols. It is now deprecated to make names that don't begin with an
+alphabetic character, and aren't alphanumeric or contain other than
+a very few other characters, namely spaces, dashes, parentheses
+and colons. Because of the added meaning of C<\N> (See L</C<\N>
+experimental regex escape>), names that look like curly brace -enclosed
+quantifiers won't work. For example, C<\N{3,4}> now means to match 3 to
+4 non-newlines; before a custom name C<3,4> could have been created.
+
+=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_12>.
+
+=over
+
+=item L<Class::ISA>
+
+=item L<Pod::Plainer>
+
+=item L<Shell>
+
+=item L<Switch>
+
+Switch is buggy and should be avoided. You may find Perl's new
+C<given>/C<when> feature a suitable replacement.  See L<perlsyn/"Switch
+statements"> for more information.
+
+=back
+
+=item Assignment to $[
+
+=item Use of the attribute :locked on subroutines
+
+=item Use of "locked" with the attributes pragma
+
+=item Use of "unique" with the attributes pragma
+
+=item Perl_pmflag
+
+C<Perl_pmflag> 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. Although listed as part of the API, it was never documented,
+and only ever used in F<toke.c>, and prior to 5.10, F<regcomp.c>. In
+core, it has been replaced by a static function.
+
+=item Numerous Perl 4-era libraries
+
+F<termcap.pl>, F<tainted.pl>, F<stat.pl>, F<shellwords.pl>, F<pwd.pl>,
+F<open3.pl>, F<open2.pl>, F<newgetopt.pl>, F<look.pl>, F<find.pl>,
+F<finddepth.pl>, F<importenv.pl>, F<hostname.pl>, F<getopts.pl>,
+F<getopt.pl>, F<getcwd.pl>, F<flush.pl>, F<fastcwd.pl>, F<exceptions.pl>,
+F<ctime.pl>, F<complete.pl>, F<cacheout.pl>, F<bigrat.pl>, F<bigint.pl>,
+F<bigfloat.pl>, F<assert.pl>, F<abbrev.pl>, F<dotsh.pl>, and
+F<timelocal.pl> are all now deprecated.  Earlier, Perl's developers
+intended to remove these libraries from Perl's core for the 5.14.0 release.
+
+During final testing before the release of 5.12.0, several developers
+discovered current production code using these ancient libraries, some
+inside the Perl core itself.  Accordingly, the pumpking granted them
+a stay of execution. They will begin to warn about their deprecation
+in the 5.14.0 release and will be removed in the 5.16.0 release.
+
+
+=back
+
+=head1 Unicode overhaul
+
+Perl's developers have made a concerted effort to update Perl to be in
+sync with the latest Unicode standard. Changes for this include:
+
+Perl can now handle every Unicode character property. New documentation,
+L<perluniprops>, lists all available non-Unihan character properties. By
+default, perl does not expose Unihan, deprecated or Unicode-internal
+properties.  See below for more details on these; there is also a section
+in the pod listing them, and explaining why they are not exposed.
+
+Perl now fully supports the Unicode compound-style of using C<=>
+and C<:> in writing regular expressions: C<\p{property=value}> and
+C<\p{property:value}> (both of which mean the same thing).
+
+Perl now fully supports the Unicode loose matching rules for text between
+the braces in C<\p{...}> constructs. In addition, Perl allows underscores
+between digits of numbers.
+
+Perl now accepts all the Unicode-defined synonyms for properties and
+property values.
+
+C<qr/\X/>, which matches a Unicode logical character, has
+been expanded to work better with various Asian languages. It
+now is defined as an I<extended grapheme cluster>. (See
+L<http://www.unicode.org/reports/tr29/>).  Anything matched previously
+and that made sense will continue to be accepted.   Additionally:
+
+=over
+
+=item *
+
+C<\X> will not break apart a C<S<CR LF>> sequence.
+
+=item *
+
+C<\X> will now match a sequence which includes the C<ZWJ> and C<ZWNJ>
+characters.
+
+=item *
+
+C<\X> will now always match at least one character, including an initial
+mark.  Marks generally come after a base character, but it is possible in
+Unicode to have them in isolation, and C<\X> will now handle that case,
+for example at the beginning of a line, or after a C<ZWSP>. And this is
+the part where C<\X> doesn't match the things that it used to that don't
+make sense. Formerly, for example, you could have the nonsensical case
+of an accented LF.
+
+=item *
+
+C<\X> will now match a (Korean) Hangul syllable sequence, and the Thai
+and Lao exception cases.
+
+=back
+
+Otherwise, this change should be transparent for the non-affected
+languages.
+
+C<\p{...}> matches using the Canonical_Combining_Class property were
+completely broken in previous releases of Perl.  They should now work
+correctly.
+
+Before Perl 5.12, the Unicode C<Decomposition_Type=Compat> property
+and a Perl extension had the same name, which led to neither matching
+all the correct values (with more than 100 mistakes in one, and several
+thousand in the other). The Perl extension has now been renamed to be
+C<Decomposition_Type=Noncanonical> (short: C<dt=noncanon>). It has the
+same meaning as was previously intended, namely the union of all the
+non-canonical Decomposition types, with Unicode C<Compat> being just
+one of those.
+
+C<\p{Decomposition_Type=Canonical}> now includes the Hangul syllables.
+
+C<\p{Uppercase}> and C<\p{Lowercase}> now work as the Unicode standard
+says they should.  This means they each match a few more characters than
+they used to.
+
+C<\p{Cntrl}> now matches the same characters as C<\p{Control}>. This
+means it no longer will match Private Use (gc=co), Surrogates (gc=cs),
+nor Format (gc=cf) code points. The Format code points represent the
+biggest possible problem. All but 36 of them are either officially
+deprecated or strongly discouraged from being used. Of those 36, likely
+the most widely used are the soft hyphen (U+00AD), and BOM, ZWSP, ZWNJ,
+WJ, and similar characters, plus bidirectional controls.
+
+C<\p{Alpha}> now matches the same characters as C<\p{Alphabetic}>. Before
+5.12, Perl's definition included a number of things that aren't
+really alpha (all marks) while omitting many that were. The definitions
+of C<\p{Alnum}> and C<\p{Word}> depend on Alpha's definition and have
+changed accordingly.
+
+C<\p{Word}> no longer incorrectly matches non-word characters such
+as fractions.
+
+C<\p{Print}> no longer matches the line control characters: Tab, LF,
+CR, FF, VT, and NEL. This brings it in line with standards and the
+documentation.
+
+C<\p{XDigit}> now matches the same characters as C<\p{Hex_Digit}>. This
+means that in addition to the characters it currently matches,
+C<[A-Fa-f0-9]>, it will also match the 22 fullwidth equivalents, for
+example U+FF10: FULLWIDTH DIGIT ZERO.
+
+The Numeric type property has been extended to include the Unihan
+characters.
+
+There is a new Perl extension, the 'Present_In', or simply 'In',
+property. This is an extension of the Unicode Age property, but
+C<\p{In=5.0}> matches any code point whose usage has been determined
+I<as of> Unicode version 5.0. The C<\p{Age=5.0}> only matches code points
+added in I<precisely> version 5.0.
+
+A number of properties now have the correct values for unassigned
+code points. The affected properties are Bidi_Class, East_Asian_Width,
+Joining_Type, Decomposition_Type, Hangul_Syllable_Type, Numeric_Type,
+and Line_Break.
+
+The Default_Ignorable_Code_Point, ID_Continue, and ID_Start properties
+are now up to date with current Unicode definitions.
+
+Earlier versions of Perl erroneously exposed certain properties that
+are supposed to be Unicode internal-only.  Use of these in regular
+expressions will now generate, if enabled, a deprecation warning message.
+The properties are: Other_Alphabetic, Other_Default_Ignorable_Code_Point,
+Other_Grapheme_Extend, Other_ID_Continue, Other_ID_Start, Other_Lowercase,
+Other_Math, and Other_Uppercase.
+
+It is now possible to change which Unicode properties Perl understands
+on a per-installation basis. As mentioned above, certain properties
+are turned off by default.  These include all the Unihan properties
+(which should be accessible via the CPAN module Unicode::Unihan) and any
+deprecated or Unicode internal-only property that Perl has never exposed.
+
+The generated files in the C<lib/unicore/To> directory are now more
+clearly marked as being stable, directly usable by applications.  New hash
+entries in them give the format of the normal entries, which allows for
+easier machine parsing. Perl can generate files in this directory for
+any property, though most are suppressed.  You can find instructions
+for changing which are written in L<perluniprops>.
+
+=head1 Modules and Pragmata
+
+=head2 New Modules and Pragmata
+
+=over 4
+
+=item C<autodie>
+
+C<autodie> is a new lexically-scoped alternative for the C<Fatal> module.
+The bundled version is 2.06_01. Note that in this release, using a string
+eval when C<autodie> is in effect can cause the autodie behaviour to leak
+into the surrounding scope. See L<autodie/"BUGS"> for more details.
+
+Version 2.06_01 has been added to the Perl core.
+
+=item C<Compress::Raw::Bzip2>
+
+Version 2.024 has been added to the Perl core.
+
+=item C<overloading>
+
+C<overloading> allows you to lexically disable or enable overloading
+for some or all operations.
+
+Version 0.001 has been added to the Perl core.
+
+=item C<parent>
+
+C<parent> establishes an ISA relationship with base classes at compile
+time. It provides the key feature of C<base> without further unwanted
+behaviors.
+
+Version 0.223 has been added to the Perl core.
+
+=item C<Parse::CPAN::Meta>
+
+Version 1.40 has been added to the Perl core.
+
+=item C<VMS::DCLsym>
+
+Version 1.03 has been added to the Perl core.
+
+=item C<VMS::Stdio>
+
+Version 2.4 has been added to the Perl core.
+
+=item C<XS::APItest::KeywordRPN>
+
+Version 0.003 has been added to the Perl core.
+
+=back
+
+=head2 Updated Pragmata
+
+=over 4
+
+=item C<base>
+
+Upgraded from version 2.13 to 2.15.
+
+=item C<bignum>
+
+Upgraded from version 0.22 to 0.23.
+
+=item C<charnames>
+
+C<charnames> now contains the Unicode F<NameAliases.txt> database file.
+This has the effect of adding some extra C<\N> character names that
+formerly wouldn't have been recognised; for example, C<"\N{LATIN CAPITAL
+LETTER GHA}">.
+
+Upgraded from version 1.06 to 1.07.
+
+=item C<constant>
+
+Upgraded from version 1.13 to 1.20.
+
+=item C<diagnostics>
+
+C<diagnostics> now supports %.0f formatting internally.
+
+C<diagnostics> no longer suppresses C<Use of uninitialized value in range
+(or flip)> warnings. [perl #71204]
+
+Upgraded from version 1.17 to 1.19.
+
+=item C<feature>
+
+In C<feature>, the meaning of the C<:5.10> and C<:5.10.X> feature
+bundles has changed slightly. The last component, if any (i.e. C<X>) is
+simply ignored.  This is predicated on the assumption that new features
+will not, in general, be added to maintenance releases. So C<:5.10>
+and C<:5.10.X> have identical effect. This is a change to the behaviour
+documented for 5.10.0.
+
+C<feature> now includes the C<unicode_strings> feature:
+
+    use feature "unicode_strings";
+
+This pragma turns on Unicode semantics for the case-changing operations
+(C<uc>, C<lc>, C<ucfirst>, C<lcfirst>) on strings that don't have the
+internal UTF-8 flag set, but that contain single-byte characters between
+128 and 255.
+
+Upgraded from version 1.11 to 1.16.
+
+=item C<less>
+
+C<less> now includes the C<stash_name> method to allow subclasses of
+C<less> to pick where in %^H to store their stash.
+
+Upgraded from version 0.02 to 0.03.
+
+=item C<lib>
+
+Upgraded from version 0.5565 to 0.62.
+
+=item C<mro>
+
+C<mro> is now implemented as an XS extension. The documented interface has
+not changed. Code relying on the implementation detail that some C<mro::>
+methods happened to be available at all times gets to "keep both pieces".
+
+Upgraded from version 1.00 to 1.02.
+
+=item C<overload>
+
+C<overload> now allow overloading of 'qr'.
+
+Upgraded from version 1.06 to 1.10.
+
+=item C<threads>
+
+Upgraded from version 1.67 to 1.75.
+
+=item C<threads::shared>
+
+Upgraded from version 1.14 to 1.32.
+
+=item C<version>
+
+C<version> now has support for L</Version number formats> as described
+earlier in this document and in its own documentation.
+
+Upgraded from version 0.74 to 0.82.
+
+=item C<warnings>
+
+C<warnings> has a new C<warnings::fatal_enabled()> function.  It also
+includes a new C<illegalproto> warning category. See also L</New or
+Changed Diagnostics> for this change.
+
+Upgraded from version 1.06 to 1.09.
+
+=back
+
+=head2 Updated Modules
+
+=over 4
+
+=item C<Archive::Extract>
+
+Upgraded from version 0.24 to 0.38.
+
+=item C<Archive::Tar>
+
+Upgraded from version 1.38 to 1.54.
+
+=item C<Attribute::Handlers>
+
+Upgraded from version 0.79 to 0.87.
+
+=item C<AutoLoader>
+
+Upgraded from version 5.63 to 5.70.
+
+=item C<B::Concise>
+
+Upgraded from version 0.74 to 0.78.
+
+=item C<B::Debug>
+
+Upgraded from version 1.05 to 1.12.
+
+=item C<B::Deparse>
+
+Upgraded from version 0.83 to 0.96.
+
+=item C<B::Lint>
+
+Upgraded from version 1.09 to 1.11_01.
+
+=item C<CGI>
+
+Upgraded from version 3.29 to 3.48.
+
+=item C<Class::ISA>
+
+Upgraded from version 0.33 to 0.36.
+
+NOTE: C<Class::ISA> is deprecated and may be removed from a future
+version of Perl.
+
+=item C<Compress::Raw::Zlib>
+
+Upgraded from version 2.008 to 2.024.
+
+=item C<CPAN>
+
+Upgraded from version 1.9205 to 1.94_56.
+
+=item C<CPANPLUS>
+
+Upgraded from version 0.84 to 0.90.
+
+=item C<CPANPLUS::Dist::Build>
+
+Upgraded from version 0.06_02 to 0.46.
+
+=item C<Data::Dumper>
+
+Upgraded from version 2.121_14 to 2.125.
+
+=item C<DB_File>
+
+Upgraded from version 1.816_1 to 1.820.
+
+=item C<Devel::PPPort>
+
+Upgraded from version 3.13 to 3.19.
+
+=item C<Digest>
+
+Upgraded from version 1.15 to 1.16.
+
+=item C<Digest::MD5>
+
+Upgraded from version 2.36_01 to 2.39.
+
+=item C<Digest::SHA>
+
+Upgraded from version 5.45 to 5.47.
+
+=item C<Encode>
+
+Upgraded from version 2.23 to 2.39.
+
+=item C<Exporter>
+
+Upgraded from version 5.62 to 5.64_01.
+
+=item C<ExtUtils::CBuilder>
+
+Upgraded from version 0.21 to 0.27.
+
+=item C<ExtUtils::Command>
+
+Upgraded from version 1.13 to 1.16.
+
+=item C<ExtUtils::Constant>
+
+Upgraded from version 0.2 to 0.22.
+
+=item C<ExtUtils::Install>
+
+Upgraded from version 1.44 to 1.55.
+
+=item C<ExtUtils::MakeMaker>
+
+Upgraded from version 6.42 to 6.56.
+
+=item C<ExtUtils::Manifest>
+
+Upgraded from version 1.51_01 to 1.57.
+
+=item C<ExtUtils::ParseXS>
+
+Upgraded from version 2.18_02 to 2.21.
+
+=item C<File::Fetch>
+
+Upgraded from version 0.14 to 0.24.
+
+=item C<File::Path>
+
+Upgraded from version 2.04 to 2.08_01.
+
+=item C<File::Temp>
+
+Upgraded from version 0.18 to 0.22.
+
+=item C<Filter::Simple>
+
+Upgraded from version 0.82 to 0.84.
+
+=item C<Filter::Util::Call>
+
+Upgraded from version 1.07 to 1.08.
+
+=item C<Getopt::Long>
+
+Upgraded from version 2.37 to 2.38.
+
+=item C<IO>
+
+Upgraded from version 1.23_01 to 1.25_02.
+
+=item C<IO::Zlib>
+
+Upgraded from version 1.07 to 1.10.
+
+=item C<IPC::Cmd>
+
+Upgraded from version 0.40_1 to 0.54.
+
+=item C<IPC::SysV>
+
+Upgraded from version 1.05 to 2.01.
+
+=item C<Locale::Maketext>
+
+Upgraded from version 1.12 to 1.14.
+
+=item C<Locale::Maketext::Simple>
+
+Upgraded from version 0.18 to 0.21.
+
+=item C<Log::Message>
+
+Upgraded from version 0.01 to 0.02.
+
+=item C<Log::Message::Simple>
+
+Upgraded from version 0.04 to 0.06.
+
+=item C<Math::BigInt>
+
+Upgraded from version 1.88 to 1.89_01.
+
+=item C<Math::BigInt::FastCalc>
+
+Upgraded from version 0.16 to 0.19.
+
+=item C<Math::BigRat>
+
+Upgraded from version 0.21 to 0.24.
+
+=item C<Math::Complex>
+
+Upgraded from version 1.37 to 1.56.
+
+=item C<Memoize>
+
+Upgraded from version 1.01_02 to 1.01_03.
+
+=item C<MIME::Base64>
+
+Upgraded from version 3.07_01 to 3.08.
+
+=item C<Module::Build>
+
+Upgraded from version 0.2808_01 to 0.3603.
+
+=item C<Module::CoreList>
+
+Upgraded from version 2.12 to 2.29.
+
+=item C<Module::Load>
+
+Upgraded from version 0.12 to 0.16.
+
+=item C<Module::Load::Conditional>
+
+Upgraded from version 0.22 to 0.34.
+
+=item C<Module::Loaded>
+
+Upgraded from version 0.01 to 0.06.
+
+=item C<Module::Pluggable>
+
+Upgraded from version 3.6 to 3.9.
+
+=item C<Net::Ping>
+
+Upgraded from version 2.33 to 2.36.
+
+=item C<NEXT>
+
+Upgraded from version 0.60_01 to 0.64.
+
+=item C<Object::Accessor>
+
+Upgraded from version 0.32 to 0.36.
+
+=item C<Package::Constants>
+
+Upgraded from version 0.01 to 0.02.
+
+=item C<PerlIO>
+
+Upgraded from version 1.04 to 1.06.
+
+=item C<Pod::Parser>
+
+Upgraded from version 1.35 to 1.37.
+
+=item C<Pod::Perldoc>
+
+Upgraded from version 3.14_02 to 3.15_02.
+
+=item C<Pod::Plainer>
+
+Upgraded from version 0.01 to 1.02.
+
+NOTE: C<Pod::Plainer> is deprecated and may be removed from a future
+version of Perl.
+
+=item C<Pod::Simple>
+
+Upgraded from version 3.05 to 3.13.
+
+=item C<Safe>
+
+Upgraded from version 2.12 to 2.22.
+
+=item C<SelfLoader>
+
+Upgraded from version 1.11 to 1.17.
+
+=item C<Storable>
+
+Upgraded from version 2.18 to 2.22.
+
+=item C<Switch>
+
+Upgraded from version 2.13 to 2.16.
+
+NOTE: C<Switch> is deprecated and may be removed from a future version
+of Perl.
+
+=item C<Sys::Syslog>
+
+Upgraded from version 0.22 to 0.27.
+
+=item C<Term::ANSIColor>
+
+Upgraded from version 1.12 to 2.02.
+
+=item C<Term::UI>
+
+Upgraded from version 0.18 to 0.20.
+
+=item C<Test>
+
+Upgraded from version 1.25 to 1.25_02.
+
+=item C<Test::Harness>
+
+Upgraded from version 2.64 to 3.17.
+
+=item C<Test::Simple>
+
+Upgraded from version 0.72 to 0.94.
+
+=item C<Text::Balanced>
+
+Upgraded from version 2.0.0 to 2.02.
+
+=item C<Text::ParseWords>
+
+Upgraded from version 3.26 to 3.27.
+
+=item C<Text::Soundex>
+
+Upgraded from version 3.03 to 3.03_01.
+
+=item C<Thread::Queue>
+
+Upgraded from version 2.00 to 2.11.
+
+=item C<Thread::Semaphore>
+
+Upgraded from version 2.01 to 2.09.
+
+=item C<Tie::RefHash>
+
+Upgraded from version 1.37 to 1.38.
+
+=item C<Time::HiRes>
+
+Upgraded from version 1.9711 to 1.9719.
+
+=item C<Time::Local>
+
+Upgraded from version 1.18 to 1.1901_01.
+
+=item C<Time::Piece>
+
+Upgraded from version 1.12 to 1.15.
+
+=item C<Unicode::Collate>
+
+Upgraded from version 0.52 to 0.52_01.
+
+=item C<Unicode::Normalize>
+
+Upgraded from version 1.02 to 1.03.
+
+=item C<Win32>
+
+Upgraded from version 0.34 to 0.39.
+
+=item C<Win32API::File>
+
+Upgraded from version 0.1001_01 to 0.1101.
+
+=item C<XSLoader>
+
+Upgraded from version 0.08 to 0.10.
+
+=back
+
+=head2 Removed Modules and Pragmata
+
+=over 4
+
+=item C<attrs>
+
+Removed from the Perl core.  Prior version was 1.02.
+
+=item C<CPAN::API::HOWTO>
+
+Removed from the Perl core.  Prior version was 'undef'.
+
+=item C<CPAN::DeferedCode>
+
+Removed from the Perl core.  Prior version was 5.50.
+
+=item C<CPANPLUS::inc>
+
+Removed from the Perl core.  Prior version was 'undef'.
+
+=item C<DCLsym>
+
+Removed from the Perl core.  Prior version was 1.03.
+
+=item C<ExtUtils::MakeMaker::bytes>
+
+Removed from the Perl core.  Prior version was 6.42.
+
+=item C<ExtUtils::MakeMaker::vmsish>
+
+Removed from the Perl core.  Prior version was 6.42.
+
+=item C<Stdio>
+
+Removed from the Perl core.  Prior version was 2.3.
+
+=item C<Test::Harness::Assert>
+
+Removed from the Perl core.  Prior version was 0.02.
+
+=item C<Test::Harness::Iterator>
+
+Removed from the Perl core.  Prior version was 0.02.
+
+=item C<Test::Harness::Point>
+
+Removed from the Perl core.  Prior version was 0.01.
+
+=item C<Test::Harness::Results>
+
+Removed from the Perl core.  Prior version was 0.01.
+
+=item C<Test::Harness::Straps>
+
+Removed from the Perl core.  Prior version was 0.26_01.
+
+=item C<Test::Harness::Util>
+
+Removed from the Perl core.  Prior version was 0.01.
+
+=item C<XSSymSet>
+
+Removed from the Perl core.  Prior version was 1.1.
+
+=back
+
+=head2 Deprecated Modules and Pragmata
+
+See L</Deprecated Modules> above.
+
+
+=head1 Documentation
+
+=head2 New Documentation
+
+=over 4
+
+=item *
+
+L<perlhaiku> contains instructions on how to build perl for the Haiku
+platform.
+
+=item *
+
+L<perlmroapi> describes the new interface for pluggable Method Resolution
+Orders.
+
+=item *
+
+L<perlperf>, by Richard Foley, provides an introduction to the use of
+performance and optimization techniques which can be used with particular
+reference to perl programs.
+
+=item *
+
+L<perlrepository> describes how to access the perl source using the I<git>
+version control system.
+
+=item *
+
+L<perlpolicy> extends the "Social contract about contributed modules" into
+the beginnings of a document on Perl porting policies.
+
+=back
+
+=head2 Changes to Existing Documentation
+
+
+=over
+
+=item *
+
+The various large F<Changes*> files (which listed every change made
+to perl over the last 18 years) have been removed, and replaced by a
+small file, also called F<Changes>, which just explains how that same
+information may be extracted from the git version control system.
+
+=item *
+
+F<Porting/patching.pod> has been deleted, as it mainly described
+interacting with the old Perforce-based repository, which is now obsolete.
+Information still relevant has been moved to L<perlrepository>.
+
+=item *
+
+The syntax C<unless (EXPR) BLOCK else BLOCK> is now documented as valid,
+as is the syntax C<unless (EXPR) BLOCK elsif (EXPR) BLOCK ... else
+BLOCK>, although actually using the latter may not be the best idea for
+the readability of your source code.
+
+=item *
+
+Documented -X overloading.
+
+=item *
+
+Documented that C<when()> treats specially most of the filetest operators
+
+=item *
+
+Documented C<when> as a syntax modifier.
+
+=item *
+
+Eliminated "Old Perl threads tutorial", which described 5005 threads.
+
+F<pod/perlthrtut.pod> is the same material reworked for ithreads.
+
+=item *
+
+Correct previous documentation: v-strings are not deprecated
+
+With version objects, we need them to use MODULE VERSION syntax. This
+patch removes the deprecation notice.
+
+=item *
+
+Security contact information is now part of L<perlsec>.
+
+=item *
+
+A significant fraction of the core documentation has been updated to
+clarify the behavior of Perl's Unicode handling.
+
+Much of the remaining core documentation has been reviewed and edited
+for clarity, consistent use of language, and to fix the spelling of Tom
+Christiansen's name.
+
+=item *
+
+The Pod specification (L<perlpodspec>) has been updated to bring the
+specification in line with modern usage already supported by most Pod
+systems. A parameter string may now follow the format name in a
+"begin/end" region. Links to URIs with a text description are now
+allowed. The usage of C<LE<lt>"section"E<gt>> has been marked as
+deprecated.
+
+=item *
+
+L<if.pm|if> has been documented in L<perlfunc/use> as a means to get
+conditional loading of modules despite the implicit BEGIN block around
+C<use>.
+
+=item *
+
+The documentation for C<$1> in perlvar.pod has been clarified.
+
+=item *
+
+C<\N{U+I<code point>}> is now documented.
+
+=back
+
+=head1 Selected Performance Enhancements
+
+=over 4
+
+=item *
+
+A new internal cache means that C<isa()> will often be faster.
+
+=item *
+
+The implementation of C<C3> Method Resolution Order has been
+optimised - linearisation for classes with single inheritance is 40%
+faster. Performance for multiple inheritance is unchanged.
+
+=item *
+
+Under C<use locale>, the locale-relevant information is now cached on
+read-only values, such as the list returned by C<keys %hash>. This makes
+operations such as C<sort keys %hash> in the scope of C<use locale>
+much faster.
+
+=item *
+
+Empty C<DESTROY> methods are no longer called.
+
+=item *
+
+C<Perl_sv_utf8_upgrade()> is now faster.
+
+=item *
+
+C<keys> on empty hash is now faster.
+
+=item *
+
+C<if (%foo)> has been optimized to be faster than C<if (keys %foo)>.
+
+=item *
+
+The string repetition operator (C<$str x $num>) is now several times
+faster when C<$str> has length one or C<$num> is large.
+
+=item *
+
+Reversing an array to itself (as in C<@a = reverse @a>) in void context
+now happens in-place and is several orders of magnitude faster than
+it used to be. It will also preserve non-existent elements whenever
+possible, i.e. for non magical arrays or tied arrays with C<EXISTS>
+and C<DELETE> methods.
+
+=back
+
+=head1 Installation and Configuration Improvements
+
+=over 4
+
+=item *
+
+L<perlapi>, L<perlintern>, L<perlmodlib> and L<perltoc> are now all
+generated at build time, rather than being shipped as part of the release.
+
+=item *
+
+If C<vendorlib> and C<vendorarch> are the same, then they are only added
+to C<@INC> once.
+
+=item *
+
+C<$Config{usedevel}> and the C-level C<PERL_USE_DEVEL> are now defined if
+perl is built with  C<-Dusedevel>.
+
+=item *
+
+F<Configure> will enable use of C<-fstack-protector>, to provide protection
+against stack-smashing attacks, if the compiler supports it.
+
+=item *
+
+F<Configure> will now determine the correct prototypes for re-entrant
+functions and for C<gconvert> if you are using a C++ compiler rather
+than a C compiler.
+
+=item *
+
+On Unix, if you build from a tree containing a git repository, the
+configuration process will note the commit hash you have checked out, for
+display in the output of C<perl -v> and C<perl -V>. Unpushed local commits
+are automatically added to the list of local patches displayed by
+C<perl -V>.
+
+=item *
+
+Perl now supports SystemTap's C<dtrace> compatibility layer and an
+issue with linking C<miniperl> has been fixed in the process.
+
+=item *
+
+perldoc now uses C<less -R> instead of C<less> for improved behaviour
+in the face of C<groff>'s new usage of ANSI escape codes.
+
+=item *
+
+
+C<perl -V> now reports use of the compile-time options C<USE_PERL_ATOF> and
+C<USE_ATTRIBUTES_FOR_PERLIO>.
+
+=item *
+
+As part of the flattening of F<ext>, all extensions on all platforms are
+built by F<make_ext.pl>. This replaces the Unix-specific
+F<ext/util/make_ext>, VMS-specific F<make_ext.com> and Win32-specific
+F<win32/buildext.pl>.
+
+=back
+
+=head1 Internal Changes
+
+Each release of Perl sees numerous internal changes which shouldn't
+affect day to day usage but may still be notable for developers working
+with Perl's source code.
+
+=over
+
+=item *
+
+The J.R.R. Tolkien quotes at the head of C source file have been checked
+and proper citations added, thanks to a patch from Tom Christiansen.
+
+=item *
+
+The internal structure of the dual-life modules traditionally found in
+the F<lib/> and F<ext/> directories in the perl source has changed
+significantly. Where possible, dual-lifed modules have been extracted
+from F<lib/> and F<ext/>.
+
+Dual-lifed modules maintained by Perl's developers as part of the Perl
+core now live in F<dist/>.  Dual-lifed modules maintained primarily on
+CPAN now live in F<cpan/>.  When reporting a bug in a module located
+under F<cpan/>, please send your bug report directly to the module's
+bug tracker or author, rather than Perl's bug tracker.
+
+=item *
+
+C<\N{...}> now compiles better, always forces UTF-8 internal representation
+
+Perl's developers have fixed several problems with the recognition of
+C<\N{...}> constructs.  As part of this, perl will store any scalar
+or regex containing C<\N{I<name>}> or C<\N{U+I<code point>}> in its
+definition in UTF-8 format. (This was true previously for all occurrences
+of C<\N{I<name>}> that did not use a custom translator, but now it's
+always true.)
+
+=item *
+
+Perl_magic_setmglob now knows about globs, fixing RT #71254.
+
+=item *
+
+C<SVt_RV> no longer exists. RVs are now stored in IVs.
+
+=item *
+
+C<Perl_vcroak()> now accepts a null first argument. In addition, a full
+audit was made of the "not NULL" compiler annotations, and those for
+several other internal functions were corrected.
+
+=item *
+
+New macros C<dSAVEDERRNO>, C<dSAVE_ERRNO>, C<SAVE_ERRNO>, C<RESTORE_ERRNO>
+have been added to formalise the temporary saving of the C<errno>
+variable.
+
+=item *
+
+The function C<Perl_sv_insert_flags> has been added to augment
+C<Perl_sv_insert>.
+
+=item *
+
+The function C<Perl_newSV_type(type)> has been added, equivalent to
+C<Perl_newSV()> followed by C<Perl_sv_upgrade(type)>.
+
+=item *
+
+The function C<Perl_newSVpvn_flags()> has been added, equivalent to
+C<Perl_newSVpvn()> and then performing the action relevant to the flag.
+
+Two flag bits are currently supported.
+
+=over 4
+
+=item *
+
+C<SVf_UTF8> will call C<SvUTF8_on()> for you. (Note that this does
+not convert a sequence of ISO 8859-1 characters to UTF-8). A wrapper,
+C<newSVpvn_utf8()> is available for this.
+
+=item *
+
+C<SVs_TEMP> now calls C<Perl_sv_2mortal()> on the new SV.
+
+=back
+
+There is also a wrapper that takes constant strings, C<newSVpvs_flags()>.
+
+=item *
+
+The function C<Perl_croak_xs_usage> has been added as a wrapper to
+C<Perl_croak>.
+
+=item *
+
+Perl now exports the functions C<PerlIO_find_layer> and C<PerlIO_list_alloc>.
+
+=item *
+
+C<PL_na> has been exterminated from the core code, replaced by local
+STRLEN temporaries, or C<*_nolen()> calls. Either approach is faster than
+C<PL_na>, which is a pointer dereference into the interpreter structure
+under ithreads, and a global variable otherwise.
+
+=item *
+
+C<Perl_mg_free()> used to leave freed memory accessible via C<SvMAGIC()>
+on the scalar. It now updates the linked list to remove each piece of
+magic as it is freed.
+
+=item *
+
+Under ithreads, the regex in C<PL_reg_curpm> is now reference
+counted. This eliminates a lot of hackish workarounds to cope with it
+not being reference counted.
+
+=item *
+
+C<Perl_mg_magical()> would sometimes incorrectly turn on C<SvRMAGICAL()>.
+This has been fixed.
+
+=item *
+
+The I<public> IV and NV flags are now not set if the string value has
+trailing "garbage". This behaviour is consistent with not setting the
+public IV or NV flags if the value is out of range for the type.
+
+=item *
+
+Uses of C<Nullav>, C<Nullcv>, C<Nullhv>, C<Nullop>, C<Nullsv> etc have
+been replaced by C<NULL> in the core code, and non-dual-life modules,
+as C<NULL> is clearer to those unfamiliar with the core code.
+
+=item *
+
+A macro C<MUTABLE_PTR(p)> has been added, which on (non-pedantic) gcc will
+not cast away C<const>, returning a C<void *>. Macros C<MUTABLE_SV(av)>,
+C<MUTABLE_SV(cv)> etc build on this, casting to C<AV *> etc without
+casting away C<const>. This allows proper compile-time auditing of
+C<const> correctness in the core, and helped picked up some errors
+(now fixed).
+
+=item *
+
+Macros C<mPUSHs()> and C<mXPUSHs()> have been added, for pushing SVs on the
+stack and mortalizing them.
+
+=item *
+
+Use of the private structure C<mro_meta> has changed slightly. Nothing
+outside the core should be accessing this directly anyway.
+
+=item *
+
+A new tool, F<Porting/expand-macro.pl> has been added, that allows you
+to view how a C preprocessor macro would be expanded when compiled.
+This is handy when trying to decode the macro hell that is the perl
+guts.
+
+=back
+
+=head1 Testing
+
+=head2 Testing improvements
+
+=over 4
+
+=item Parallel tests
+
+The core distribution can now run its regression tests in parallel on
+Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS> in
+your environment to the number of tests to run in parallel, and run
+C<make test_harness>. On a Bourne-like shell, this can be done as
+
+    TEST_JOBS=3 make test_harness  # Run 3 tests in parallel
+
+An environment variable is used, rather than parallel make itself, because
+L<TAP::Harness> needs to be able to schedule individual non-conflicting test
+scripts itself, and there is no standard interface to C<make> utilities to
+interact with their job schedulers.
+
+Note that currently some test scripts may fail when run in parallel (most
+notably C<ext/IO/t/io_dir.t>). If necessary run just the failing scripts
+again sequentially and see if the failures go away.
+
+=item Test harness flexibility
+
+It's now possible to override C<PERL5OPT> and friends in F<t/TEST>
+
+=item Test watchdog
+
+Several tests that have the potential to hang forever if they fail now
+incorporate a "watchdog" functionality that will kill them after a timeout,
+which helps ensure that C<make test> and C<make test_harness> run to
+completion automatically.
+
+
+=back
+
+=head2 New Tests
+
+Perl's developers have added a number of new tests to the core.
+In addition to the items listed below, many modules updated from CPAN
+incorporate new tests.
+
+=over 4
+
+=item *
+
+Significant cleanups to core tests to ensure that language and
+interpreter features are not used before they're tested.
+
+=item *
+
+C<make test_porting> now runs a number of important pre-commit checks
+which might be of use to anyone working on the Perl core.
+
+=item *
+
+F<t/porting/podcheck.t> automatically checks the well-formedness of
+POD found in all .pl, .pm and .pod files in the F<MANIFEST>, other than in
+dual-lifed modules which are primarily maintained outside the Perl core.
+
+=item *
+
+F<t/porting/manifest.t> now tests that all files listed in MANIFEST
+are present.
+
+=item *
+
+F<t/op/while_readdir.t> tests that a bare readdir in while loop sets $_.
+
+=item *
+
+F<t/comp/retainedlines.t> checks that the debugger can retain source
+lines from C<eval>.
+
+=item *
+
+F<t/io/perlio_fail.t> checks that bad layers fail.
+
+=item *
+
+F<t/io/perlio_leaks.t> checks that PerlIO layers are not leaking.
+
+=item *
+
+F<t/io/perlio_open.t> checks that certain special forms of open work.
+
+=item *
+
+F<t/io/perlio.t> includes general PerlIO tests.
+
+=item *
+
+F<t/io/pvbm.t> checks that there is no unexpected interaction between
+the internal types C<PVBM> and C<PVGV>.
+
+=item *
+
+F<t/mro/package_aliases.t> checks that mro works properly in the presence
+of aliased packages.
+
+=item *
+
+F<t/op/dbm.t> tests C<dbmopen> and C<dbmclose>.
+
+=item *
+
+F<t/op/index_thr.t> tests the interaction of C<index> and threads.
+
+=item *
+
+F<t/op/pat_thr.t> tests the interaction of esoteric patterns and threads.
+
+=item *
+
+F<t/op/qr_gc.t> tests that C<qr> doesn't leak.
+
+=item *
+
+F<t/op/reg_email_thr.t> tests the interaction of regex recursion and threads.
+
+=item *
+
+F<t/op/regexp_qr_embed_thr.t> tests the interaction of patterns with
+embedded C<qr//> and threads.
+
+=item *
+
+F<t/op/regexp_unicode_prop.t> tests Unicode properties in regular
+expressions.
+
+=item *
+
+F<t/op/regexp_unicode_prop_thr.t> tests the interaction of Unicode
+properties and threads.
+
+=item *
+
+F<t/op/reg_nc_tie.t> tests the tied methods of C<Tie::Hash::NamedCapture>.
+
+=item *
+
+F<t/op/reg_posixcc.t> checks that POSIX character classes behave
+consistently.
+
+=item *
+
+F<t/op/re.t> checks that exportable C<re> functions in F<universal.c> work.
+
+=item *
+
+F<t/op/setpgrpstack.t> checks that C<setpgrp> works.
+
+=item *
+
+F<t/op/substr_thr.t> tests the interaction of C<substr> and threads.
+
+=item *
+
+F<t/op/upgrade.t> checks that upgrading and assigning scalars works.
+
+=item *
+
+F<t/uni/lex_utf8.t> checks that Unicode in the lexer works.
+
+=item *
+
+F<t/uni/tie.t> checks that Unicode and C<tie> work.
+
+=item *
+
+F<t/comp/final_line_num.t> tests whether line numbers are correct at EOF
+
+=item *
+
+F<t/comp/form_scope.t> tests format scoping.
+
+=item *
+
+F<t/comp/line_debug.t> tests whether C<< @{"_<$file"} >> works.
+
+=item *
+
+F<t/op/filetest_t.t> tests if -t file test works.
+
+=item *
+
+F<t/op/qr.t> tests C<qr>.
+
+=item *
+
+F<t/op/utf8cache.t> tests malfunctions of the utf8 cache.
+
+=item *
+
+F<t/re/uniprops.t> test unicodes C<\p{}> regex constructs.
+
+=item *
+
+F<t/op/filehandle.t> tests some suitably portable filetest operators
+to check that they work as expected, particularly in the light of some
+internal changes made in how filehandles are blessed.
+
+=item *
+
+F<t/op/time_loop.t> tests that unix times greater than C<2**63>, which
+can now be handed to C<gmtime> and C<localtime>, do not cause an internal
+overflow or an excessively long loop.
+
+=back
+
+
+=head1 New or Changed Diagnostics
+
+=head2 New Diagnostics
+
+=over
+
+=item *
+
+SV allocation tracing has been added to the diagnostics enabled by C<-Dm>.
+The tracing can alternatively output via the C<PERL_MEM_LOG> mechanism, if
+that was enabled when the F<perl> binary was compiled.
+
+=item *
+
+Smartmatch resolution tracing has been added as a new diagnostic. Use
+C<-DM> to enable it.
+
+=item *
+
+A new debugging flag C<-DB> now dumps subroutine definitions, leaving
+C<-Dx> for its original purpose of dumping syntax trees.
+
+=item *
+
+Perl 5.12 provides a number of new diagnostic messages to help you write
+better code.  See L<perldiag> for details of these new messages.
+
+=over 4
+
+=item *
+
+C<Bad plugin affecting keyword '%s'>
+
+=item *
+
+C<gmtime(%.0f) too large>
+
+=item *
+
+C<Lexing code attempted to stuff non-Latin-1 character into Latin-1 input>
+
+=item *
+
+C<Lexing code internal error (%s)>
+
+=item *
+
+C<localtime(%.0f) too large>
+
+=item *
+
+C<Overloaded dereference did not return a reference>
+
+=item *
+
+C<Overloaded qr did not return a REGEXP>
+
+=item *
+
+C<Perl_pmflag() is deprecated, and will be removed from the XS API>
+
+=item *
+
+C<lvalue attribute ignored after the subroutine has been defined>
+
+This new warning is issued when one attempts to mark a subroutine as
+lvalue after it has been defined.
+
+=item *
+
+Perl now warns you if C<++> or C<--> are unable to change the value
+because it's beyond the limit of representation.
+
+This uses a new warnings category: "imprecision".
+
+=item *
+
+C<lc>, C<uc>, C<lcfirst>, and C<ucfirst> warn when passed undef.
+
+=item *
+
+C<Show constant in "Useless use of a constant in void context">
+
+=item *
+
+C<Prototype after '%s'>
+
+=item *
+
+C<panic: sv_chop %s>
+
+This new fatal error occurs when the C routine C<Perl_sv_chop()> was
+passed a position that is not within the scalar's string buffer. This
+could be caused by buggy XS code, and at this point recovery is not
+possible.
+
+=item *
+
+The fatal error C<Malformed UTF-8 returned by \N> is now produced if the
+C<charnames> handler returns malformed UTF-8.
+
+=item *
+
+If an unresolved named character or sequence was encountered when
+compiling a regex pattern then the fatal error C<\N{NAME} must be resolved
+by the lexer> is now produced. This can happen, for example, when using a
+single-quotish context like C<$re = '\N{SPACE}'; /$re/;>. See L<perldiag>
+for more examples of how the lexer can get bypassed.
+
+=item *
+
+C<Invalid hexadecimal number in \N{U+...}> is a new fatal error
+triggered when the character constant represented by C<...> is not a
+valid hexadecimal number.
+
+=item *
+
+The new meaning of C<\N> as C<[^\n]> is not valid in a bracketed character
+class, just like C<.> in a character class loses its special meaning,
+and will cause the fatal error C<\N in a character class must be a named
+character: \N{...}>.
+
+=item *
+
+The rules on what is legal for the C<...> in C<\N{...}> have been
+tightened up so that unless the C<...> begins with an alphabetic
+character and continues with a combination of alphanumerics, dashes,
+spaces, parentheses or colons then the warning C<Deprecated character(s)
+in \N{...} starting at '%s'> is now issued.
+
+=item *
+
+The warning C<Using just the first characters returned by \N{}> will
+be issued if the C<charnames> handler returns a sequence of characters
+which exceeds the limit of the number of characters that can be used. The
+message will indicate which characters were used and which were discarded.
+
+=back
+
+=back
+
+=head2 Changed Diagnostics
+
+A number of existing diagnostic messages have been improved or corrected:
+
+=over
+
+=item *
+
+A new warning category C<illegalproto> allows finer-grained control of
+warnings around function prototypes.
+
+The two warnings:
+
+=over
+
+=item C<Illegal character in prototype for %s : %s>
+
+=item C<Prototype after '%c' for %s : %s>
+
+=back
+
+have been moved from the C<syntax> top-level warnings category into a new
+first-level category, C<illegalproto>. These two warnings are currently
+the only ones emitted during parsing of an invalid/illegal prototype,
+so one can now use
+
+  no warnings 'illegalproto';
+
+to suppress only those, but not other syntax-related warnings. Warnings
+where prototypes are changed, ignored, or not met are still in the
+C<prototype> category as before.
+
+=item *
+
+C<Deep recursion on subroutine "%s">
+
+It is now possible to change the depth threshold for this warning from the
+default of 100, by recompiling the F<perl> binary, setting the C
+pre-processor macro C<PERL_SUB_DEPTH_WARN> to the desired value.
+
+=item *
+
+C<Illegal character in prototype> warning is now more precise
+when reporting illegal characters after _
+
+=item *
+
+mro merging error messages are now very similar to those produced by
+L<Algorithm::C3>.
+
+=item *
+
+Amelioration of the error message "Unrecognized character %s in column %d"
+
+Changes the error message to "Unrecognized character %s; marked by E<lt>--
+HERE after %sE<lt>-- HERE near column %d". This should make it a little
+simpler to spot and correct the suspicious character.
+
+=item *
+
+Perl now explicitly points to C<$.> when it causes an uninitialized
+warning for ranges in scalar context.
+
+=item *
+
+C<split> now warns when called in void context.
+
+=item *
+
+C<printf>-style functions called with too few arguments will now issue the
+warning C<"Missing argument in %s"> [perl #71000]
+
+=item *
+
+Perl now properly returns a syntax error instead of segfaulting
+if C<each>, C<keys>, or C<values> is used without an argument.
+
+=item *
+
+C<tell()> now fails properly if called without an argument and when no
+previous file was read.
+
+C<tell()> now returns C<-1>, and sets errno to C<EBADF>, thus restoring
+the 5.8.x behaviour.
+
+=item *
+
+C<overload> no longer implicitly unsets fallback on repeated 'use
+overload' lines.
+
+=item *
+
+POSIX::strftime() can now handle Unicode characters in the format string.
+
+=item *
+
+The C<syntax> category was removed from 5 warnings that should only be in
+C<deprecated>.
+
+=item *
+
+Three fatal C<pack>/C<unpack> error messages have been normalized to
+C<panic: %s>
+
+=item *
+
+C<Unicode character is illegal> has been rephrased to be more accurate
+
+It now reads C<Unicode non-character is illegal in interchange> and the
+perldiag documentation has been expanded a bit.
+
+=item *
+
+Currently, all but the first of the several characters that the
+C<charnames> handler may return are discarded when used in a regular
+expression pattern bracketed character class. If this happens then the
+warning C<Using just the first character returned by \N{} in character
+class> will be issued.
+
+=item *
+
+The warning C<Missing right brace on \N{} or unescaped left brace after
+\N.  Assuming the latter> will be issued if Perl encounters a C<\N{>
+but doesn't find a matching C<}>. In this case Perl doesn't know if it
+was mistakenly omitted, or if "match non-newline" followed by "match
+a C<{>" was desired.  It assumes the latter because that is actually a
+valid interpretation as written, unlike the other case.  If you meant
+the former, you need to add the matching right brace.  If you did mean
+the latter, you can silence this warning by writing instead C<\N\{>.
+
+=item *
+
+C<gmtime> and C<localtime> called with numbers smaller than they can
+reliably handle will now issue the warnings C<gmtime(%.0f) too small>
+and C<localtime(%.0f) too small>.
+
+=back
+
+The following diagnostic messages have been removed:
+
+=over 4
+
+=item *
+
+C<Runaway format>
+
+=item *
+
+C<Can't locate package %s for the parents of %s>
+
+In general this warning it only got produced in
+conjunction with other warnings, and removing it allowed an ISA lookup
+optimisation to be added.
+
+=item *
+
+C<v-string in use/require is non-portable>
+
+=back
+
+=head1 Utility Changes
+
+=over 4
+
+=item *
+
+F<h2ph> now looks in C<include-fixed> too, which is a recent addition
+to gcc's search path.
+
+=item *
+
+F<h2xs> no longer incorrectly treats enum values like macros.
+It also now handles C++ style comments (C<//>) properly in enums.
+
+=item *
+
+F<perl5db.pl> now supports C<LVALUE> subroutines.  Additionally, the
+debugger now correctly handles proxy constant subroutines, and
+subroutine stubs.
+
+=item *
+
+F<perlbug> now uses C<%Module::CoreList::bug_tracker> to print out
+upstream bug tracker URLs.  If a user identifies a particular module
+as the topic of their bug report and we're able to divine the URL for
+its upstream bug tracker, perlbug now provide a message to the user
+explaining that the core copies the CPAN version directly, and provide
+the URL for reporting the bug directly to the upstream author.
+
+F<perlbug> no longer reports "Message sent" when it hasn't actually sent
+the message
+
+=item *
+
+F<perlthanks> is a new utility for sending non-bug-reports to the
+authors and maintainers of Perl. Getting nothing but bug reports can
+become a bit demoralising. If Perl 5.12 works well for you, please try
+out F<perlthanks>. It will make the developers smile.
+
+=item *
+
+Perl's developers have fixed bugs in F<a2p> having to do with the
+C<match()> operator in list context.  Additionally, F<a2p> no longer
+generates code that uses the C<$[> variable.
+
+=back
+
+=head1 Selected Bug Fixes
+
+=over 4
+
+=item *
+
+U+0FFFF is now a legal character in regular expressions.
+
+=item *
+
+pp_qr now always returns a new regexp SV. Resolves RT #69852.
+
+Instead of returning a(nother) reference to the (pre-compiled) regexp
+in the optree, use reg_temp_copy() to create a copy of it, and return a
+reference to that. This resolves issues about Regexp::DESTROY not being
+called in a timely fashion (the original bug tracked by RT #69852), as
+well as bugs related to blessing regexps, and of assigning to regexps,
+as described in correspondence added to the ticket.
+
+It transpires that we also need to undo the SvPVX() sharing when ithreads
+cloning a Regexp SV, because mother_re is set to NULL, instead of a
+cloned copy of the mother_re. This change might fix bugs with regexps
+and threads in certain other situations, but as yet neither tests nor
+bug reports have indicated any problems, so it might not actually be an
+edge case that it's possible to reach.
+
+=item *
+
+Several compilation errors and segfaults when perl was built with C<-Dmad>
+were fixed.
+
+=item *
+
+Fixes for lexer API changes in 5.11.2 which broke NYTProf's savesrc option.
+
+=item *
+
+C<-t> should only return TRUE for file handles connected to a TTY
+
+The Microsoft C version of C<isatty()> returns TRUE for all character mode
+devices, including the F</dev/null>-style "nul" device and printers like
+"lpt1".
+
+=item *
+
+Fixed a regression caused by commit fafafbaf which caused a panic during
+parameter passing [perl #70171]
+
+=item *
+
+On systems which in-place edits without backup files, -i'*' now works as
+the documentation says it does [perl #70802]
+
+=item *
+
+Saving and restoring magic flags no longer loses readonly flag.
+
+=item *
+
+The malformed syntax C<grep EXPR LIST> (note the missing comma) no longer
+causes abrupt and total failure.
+
+=item *
+
+Regular expressions compiled with C<qr{}> literals properly set C<$'> when
+matching again.
+
+=item *
+
+Using named subroutines with C<sort> should no longer lead to bus errors
+[perl #71076]
+
+=item *
+
+Numerous bugfixes catch small issues caused by the recently-added Lexer API.
+
+=item *
+
+Smart match against C<@_> sometimes gave false negatives. [perl #71078]
+
+=item *
+
+C<$@> may now be assigned a read-only value (without error or busting
+the stack).
+
+=item *
+
+C<sort> called recursively from within an active comparison subroutine no
+longer causes a bus error if run multiple times. [perl #71076]
+
+=item *
+
+Tie::Hash::NamedCapture::* will not abort if passed bad input (RT #71828)
+
+=item *
+
+@_ and $_ no longer leak under threads (RT #34342 and #41138, also
+#70602, #70974)
+
+=item *
+
+C<-I> on shebang line now adds directories in front of @INC
+as documented, and as does C<-I> when specified on the command-line.
+
+=item *
+
+C<kill> is now fatal when called on non-numeric process identifiers.
+Previously, an C<undef> process identifier would be interpreted as a
+request to kill process 0, which would terminate the current process
+group on POSIX systems. Since process identifiers are always integers,
+killing a non-numeric process is now fatal.
+
+=item *
+
+5.10.0 inadvertently disabled an optimisation, which caused a measurable
+performance drop in list assignment, such as is often used to assign
+function parameters from C<@_>. The optimisation has been re-instated, and
+the performance regression fixed. (This fix is also present in 5.10.1)
+
+=item *
+
+Fixed memory leak on C<while (1) { map 1, 1 }> [RT #53038].
+
+=item *
+
+Some potential coredumps in PerlIO fixed [RT #57322,54828].
+
+=item *
+
+The debugger now works with lvalue subroutines.
+
+=item *
+
+The debugger's C<m> command was broken on modules that defined constants
+[RT #61222].
+
+=item *
+
+C<crypt> and string complement could return tainted values for untainted
+arguments [RT #59998].
+
+=item *
+
+The C<-i>I<.suffix> command-line switch now recreates the file using
+restricted permissions, before changing its mode to match the original
+file. This eliminates a potential race condition [RT #60904].
+
+=item *
+
+On some Unix systems, the value in C<$?> would not have the top bit set
+(C<$? & 128>) even if the child core dumped.
+
+=item *
+
+Under some circumstances, C<$^R> could incorrectly become undefined
+[RT #57042].
+
+=item *
+
+In the XS API, various hash functions, when passed a pre-computed hash where
+the key is UTF-8, might result in an incorrect lookup.
+
+=item *
+
+XS code including F<XSUB.h> before F<perl.h> gave a compile-time error
+[RT #57176].
+
+=item *
+
+C<< $object-E<gt>isa('Foo') >> would report false if the package C<Foo>
+didn't exist, even if the object's C<@ISA> contained C<Foo>.
+
+=item *
+
+Various bugs in the new-to 5.10.0 mro code, triggered by manipulating
+C<@ISA>, have been found and fixed.
+
+=item *
+
+Bitwise operations on references could crash the interpreter, e.g.
+C<$x=\$y; $x |= "foo"> [RT #54956].
+
+=item *
+
+Patterns including alternation might be sensitive to the internal UTF-8
+representation, e.g.
+
+    my $byte = chr(192);
+    my $utf8 = chr(192); utf8::upgrade($utf8);
+    $utf8 =~ /$byte|X}/i;      # failed in 5.10.0
+
+=item *
+
+Within UTF8-encoded Perl source files (i.e. where C<use utf8> is in
+effect), double-quoted literal strings could be corrupted where a C<\xNN>,
+C<\0NNN> or C<\N{}> is followed by a literal character with ordinal value
+greater than 255 [RT #59908].
+
+=item *
+
+C<B::Deparse> failed to correctly deparse various constructs:
+C<readpipe STRING> [RT #62428], C<CORE::require(STRING)> [RT #62488],
+C<sub foo(_)> [RT #62484].
+
+=item *
+
+Using C<setpgrp> with no arguments could corrupt the perl stack.
+
+=item *
+
+The block form of C<eval> is now specifically trappable by C<Safe> and
+C<ops>. Previously it was erroneously treated like string C<eval>.
+
+=item *
+
+In 5.10.0, the two characters C<[~> were sometimes parsed as the smart
+match operator (C<~~>) [RT #63854].
+
+=item *
+
+In 5.10.0, the C<*> quantifier in patterns was sometimes treated as
+C<{0,32767}> [RT #60034, #60464]. For example, this match would fail:
+
+    ("ab" x 32768) =~ /^(ab)*$/
+
+=item *
+
+C<shmget> was limited to a 32 bit segment size on a 64 bit OS [RT #63924].
+
+=item *
+
+Using C<next> or C<last> to exit a C<given> block no longer produces a
+spurious warning like the following:
+
+    Exiting given via last at foo.pl line 123
+
+=item *
+
+Assigning a format to a glob could corrupt the format; e.g.:
+
+     *bar=*foo{FORMAT}; # foo format now bad
+
+=item *
+
+Attempting to coerce a typeglob to a string or number could cause an
+assertion failure. The correct error message is now generated,
+C<Can't coerce GLOB to I<$type>>.
+
+=item *
+
+Under C<use filetest 'access'>, C<-x> was using the wrong access
+mode. This has been fixed [RT #49003].
+
+=item *
+
+C<length> on a tied scalar that returned a Unicode value would not be
+correct the first time. This has been fixed.
+
+=item *
+
+Using an array C<tie> inside in array C<tie> could SEGV. This has been
+fixed. [RT #51636]
+
+=item *
+
+A race condition inside C<PerlIOStdio_close()> has been identified and
+fixed. This used to cause various threading issues, including SEGVs.
+
+=item *
+
+In C<unpack>, the use of C<()> groups in scalar context was internally
+placing a list on the interpreter's stack, which manifested in various
+ways, including SEGVs. This is now fixed [RT #50256].
+
+=item *
+
+Magic was called twice in C<substr>, C<\&$x>, C<tie $x, $m> and C<chop>.
+These have all been fixed.
+
+=item *
+
+A 5.10.0 optimisation to clear the temporary stack within the implicit
+loop of C<s///ge> has been reverted, as it turned out to be the cause of
+obscure bugs in seemingly unrelated parts of the interpreter [commit
+ef0d4e17921ee3de].
+
+=item *
+
+The line numbers for warnings inside C<elsif> are now correct.
+
+=item *
+
+The C<..> operator now works correctly with ranges whose ends are at or
+close to the values of the smallest and largest integers.
+
+=item *
+
+C<binmode STDIN, ':raw'> could lead to segmentation faults on some platforms.
+This has been fixed [RT #54828].
+
+=item *
+
+An off-by-one error meant that C<index $str, ...> was effectively being
+executed as C<index "$str\0", ...>. This has been fixed [RT #53746].
+
+=item *
+
+Various leaks associated with named captures in regexes have been fixed
+[RT #57024].
+
+=item *
+
+A weak reference to a hash would leak. This was affecting C<DBI>
+[RT #56908].
+
+=item *
+
+Using (?|) in a regex could cause a segfault [RT #59734].
+
+=item *
+
+Use of a UTF-8 C<tr//> within a closure could cause a segfault [RT #61520].
+
+=item *
+
+Calling C<Perl_sv_chop()> or otherwise upgrading an SV could result in an
+unaligned 64-bit access on the SPARC architecture [RT #60574].
+
+=item *
+
+In the 5.10.0 release, C<inc_version_list> would incorrectly list
+C<5.10.*> after C<5.8.*>; this affected the C<@INC> search order
+[RT #67628].
+
+=item *
+
+In 5.10.0, C<pack "a*", $tainted_value> returned a non-tainted value
+[RT #52552].
+
+=item *
+
+In 5.10.0, C<printf> and C<sprintf> could produce the fatal error
+C<panic: utf8_mg_pos_cache_update> when printing UTF-8 strings
+[RT #62666].
+
+=item *
+
+In the 5.10.0 release, a dynamically created C<AUTOLOAD> method might be
+missed (method cache issue) [RT #60220,60232].
+
+=item *
+
+In the 5.10.0 release, a combination of C<use feature> and C<//ee> could
+cause a memory leak [RT #63110].
+
+=item *
+
+C<-C> on the shebang (C<#!>) line is once more permitted if it is also
+specified on the command line. C<-C> on the shebang line used to be a
+silent no-op I<if> it was not also on the command line, so perl 5.10.0
+disallowed it, which broke some scripts. Now perl checks whether it is
+also on the command line and only dies if it is not [RT #67880].
+
+=item *
+
+In 5.10.0, certain types of re-entrant regular expression could crash,
+or cause the following assertion failure [RT #60508]:
+
+    Assertion rx->sublen >= (s - rx->subbeg) + i failed
+
+=item *
+
+Perl now includes previously missing files from the Unicode Character
+Database.
+
+=item *
+
+Perl now honors C<TMPDIR> when opening an anonymous temporary file.
+
+=back
+
+
+=head1 Platform Specific Changes
+
+Perl is incredibly portable. In general, if a platform has a C compiler,
+someone has ported Perl to it (or will soon).  We're happy to announce
+that Perl 5.12 includes support for several new platforms.  At the same
+time, it's time to bid farewell to some (very) old friends.
+
+=head2 New Platforms
+
+=over
+
+=item Haiku
+
+Perl's developers have merged patches from Haiku's maintainers. Perl
+should now build on Haiku.
+
+=item MirOS BSD
+
+Perl should now build on MirOS BSD.
+
+=back
+
+=head2 Discontinued Platforms
+
+=over
+
+=item Domain/OS
+
+=item MiNT
+
+=item Tenon MachTen
+
+=back
+
+=head2 Updated Platforms
+
+=over 4
+
+=item AIX
+
+=over 4
+
+=item *
+
+Removed F<libbsd> for AIX 5L and 6.1. Only C<flock()> was used from
+F<libbsd>.
+
+=item *
+
+Removed F<libgdbm> for AIX 5L and 6.1 if F<libgdbm> < 1.8.3-5 is
+installed.  The F<libgdbm> is delivered as an optional package with the
+AIX Toolbox.  Unfortunately the versions below 1.8.3-5 are broken.
+
+=item *
+
+Hints changes mean that AIX 4.2 should work again.
+
+=back
+
+=item Cygwin
+
+=over 4
+
+=item *
+
+Perl now supports IPv6 on Cygwin 1.7 and newer.
+
+=item *
+
+On Cygwin we now strip the last number from the DLL. This has been the
+behaviour in the cygwin.com build for years. The hints files have been
+updated.
+
+=back
+
+=item Darwin (Mac OS X)
+
+=over 4
+
+=item *
+
+Skip testing the be_BY.CP1131 locale on Darwin 10 (Mac OS X 10.6),
+as it's still buggy.
+
+=item *
+
+Correct infelicities in the regexp used to identify buggy locales
+on Darwin 8 and 9 (Mac OS X 10.4 and 10.5, respectively).
+
+=back
+
+=item DragonFly BSD
+
+=over 4
+
+=item *
+
+Fix thread library selection [perl #69686]
+
+=back
+
+=item FreeBSD
+
+=over 4
+
+=item *
+
+The hints files now identify the correct threading libraries on FreeBSD 7
+and later.
+
+=back
+
+=item Irix
+
+=over 4
+
+=item *
+
+We now work around a bizarre preprocessor bug in the Irix 6.5 compiler:
+C<cc -E -> unfortunately goes into K&R mode, but C<cc -E file.c> doesn't.
+
+=back
+
+=item NetBSD
+
+=over 4
+
+=item *
+
+Hints now supports versions 5.*.
+
+=back
+
+=item OpenVMS
+
+=over 4
+
+=item *
+
+C<-UDEBUGGING> is now the default on VMS.
+
+Like it has been everywhere else for ages and ages. Also make command-line
+selection of -UDEBUGGING and -DDEBUGGING work in configure.com; before
+the only way to turn it off was by saying no in answer to the interactive
+question.
+
+=item *
+
+The default pipe buffer size on VMS has been updated to 8192 on 64-bit
+systems.
+
+=item *
+
+Reads from the in-memory temporary files of C<PerlIO::scalar> used to fail
+if C<$/> was set to a numeric reference (to indicate record-style reads).
+This is now fixed.
+
+=item *
+
+VMS now supports C<getgrgid>.
+
+=item *
+
+Many improvements and cleanups have been made to the VMS file name handling
+and conversion code.
+
+=item *
+
+Enabling the C<PERL_VMS_POSIX_EXIT> logical name now encodes a POSIX exit
+status in a VMS condition value for better interaction with GNV's bash
+shell and other utilities that depend on POSIX exit values. See
+L<perlvms/"$?"> for details.
+
+=item *
+
+C<File::Copy> now detects Unix compatibility mode on VMS.
+
+=back
+
+=item Stratus VOS
+
+=over 4
+
+=item *
+
+Various changes from Stratus have been merged in.
+
+=back
+
+=item Symbian
+
+=over 4
+
+=item *
+
+There is now support for Symbian S60 3.2 SDK and S60 5.0 SDK.
+
+=back
+
+=item Windows
+
+=over 4
+
+=item *
+
+Perl 5.12 supports Windows 2000 and later. The supporting code for
+legacy versions of Windows is still included, but will be removed
+during the next development cycle.
+
+=item *
+
+Initial support for building Perl with MinGW-w64 is now available.
+
+=item *
+
+F<perl.exe> now includes a manifest resource to specify the C<trustInfo>
+settings for Windows Vista and later. Without this setting Windows
+would treat F<perl.exe> as a legacy application and apply various
+heuristics like redirecting access to protected file system areas
+(like the "Program Files" folder) to the users "VirtualStore"
+instead of generating a proper "permission denied" error.
+
+The manifest resource also requests the Microsoft Common-Controls
+version 6.0 (themed controls introduced in Windows XP).  Check out the
+Win32::VisualStyles module on CPAN to switch back to old style
+unthemed controls for legacy applications.
+
+=item *
+
+The C<-t> filetest operator now only returns true if the filehandle
+is connected to a console window.  In previous versions of Perl it
+would return true for all character mode devices, including F<NUL>
+and F<LPT1>.
+
+=item *
+
+The C<-p> filetest operator now works correctly, and the
+Fcntl::S_IFIFO constant is defined when Perl is compiled with
+Microsoft Visual C.  In previous Perl versions C<-p> always
+returned a false value, and the Fcntl::S_IFIFO constant
+was not defined.
+
+This bug is specific to Microsoft Visual C and never affected
+Perl binaries built with MinGW.
+
+=item *
+
+The socket error codes are now more widely supported:  The POSIX
+module will define the symbolic names, like POSIX::EWOULDBLOCK,
+and stringification of socket error codes in $! works as well
+now;
+
+  C:\>perl -MPOSIX -E "$!=POSIX::EWOULDBLOCK; say $!"
+  A non-blocking socket operation could not be completed immediately.
+
+=item *
+
+flock() will now set sensible error codes in $!.  Previous Perl versions
+copied the value of $^E into $!, which caused much confusion.
+
+=item *
+
+select() now supports all empty C<fd_set>s more correctly.
+
+=item *
+
+C<'.\foo'> and C<'..\foo'>  were treated differently than
+C<'./foo'> and C<'../foo'> by C<do> and C<require> [RT #63492].
+
+=item *
+
+Improved message window handling means that C<alarm> and C<kill> messages
+will no longer be dropped under race conditions.
+
+=item *
+
+Various bits of Perl's build infrastructure are no longer converted to
+win32 line endings at release time. If this hurts you, please report the
+problem with the L<perlbug> program included with perl.
+
+=back
+
+=back
+
+
+=head1 Known Problems
+
+This is a list of some significant unfixed bugs, which are regressions
+from either 5.10.x or 5.8.x.
+
+=over 4
+
+=item *
+
+Some CPANPLUS tests may fail if there is a functioning file
+F<../../cpanp-run-perl> outside your build directory. The failure
+shouldn't imply there's a problem with the actual functional
+software. The bug is already fixed in [RT #74188] and is scheduled for
+inclusion in perl-v5.12.1.
+
+=item *
+
+C<List::Util::first> misbehaves in the presence of a lexical C<$_>
+(typically introduced by C<my $_> or implicitly by C<given>). The variable
+which gets set for each iteration is the package variable C<$_>, not the
+lexical C<$_> [RT #67694].
+
+A similar issue may occur in other modules that provide functions which
+take a block as their first argument, like
+
+    foo { ... $_ ...} list
+
+=item *
+
+Some regexes may run much more slowly when run in a child thread compared
+with the thread the pattern was compiled into [RT #55600].
+
+=item *
+
+Things like C<"\N{LATIN SMALL LIGATURE FF}" =~ /\N{LATIN SMALL LETTER F}+/>
+will appear to hang as they get into a very long running loop [RT #72998].
+
+=item *
+
+Several porters have reported mysterious crashes when Perl's entire
+test suite is run after a build on certain Windows 2000 systems. When
+run by hand, the individual tests reportedly work fine.
+
+=back
+
+=head1 Errata
+
+=over
+
+=item *
+
+This one is actually a change introduced in 5.10.0, but it was missed
+from that release's perldelta, so it is mentioned here instead.
+
+A bugfix related to the handling of the C</m> modifier and C<qr> resulted
+in a change of behaviour between 5.8.x and 5.10.0:
+
+    # matches in 5.8.x, doesn't match in 5.10.0
+    $re = qr/^bar/; "foo\nbar" =~ /$re/m;
+
+=back
+
+=head1 Acknowledgements
+
+Perl 5.12.0 represents approximately two years of development since
+Perl 5.10.0 and contains over 750,000 lines of changes across over
+3,000 files from over 200 authors and committers.
+
+Perl continues to flourish into its third decade thanks to a vibrant
+community of users and developers.  The following people are known to
+have contributed the improvements that became Perl 5.12.0:
+
+Aaron Crane, Abe Timmerman, Abhijit Menon-Sen, Abigail, Adam Russell,
+Adriano Ferreira, Ævar Arnfjörð Bjarmason, Alan Grover, Alexandr
+Ciornii, Alex Davies, Alex Vandiver, Andreas Koenig, Andrew Rodland,
+andrew@sundale.net, Andy Armstrong, Andy Dougherty, Jose AUGUSTE-ETIENNE,
+Benjamin Smith, Ben Morrow, bharanee rathna, Bo Borgerson, Bo Lindbergh,
+Brad Gilbert, Bram, Brendan O'Dea, brian d foy, Charles Bailey,
+Chip Salzenberg, Chris 'BinGOs' Williams, Christoph Lamprecht, Chris
+Williams, chromatic, Claes Jakobsson, Craig A. Berry, Dan Dascalescu,
+Daniel Frederick Crisman, Daniel M. Quinlan, Dan Jacobson, Dan Kogai,
+Dave Mitchell, Dave Rolsky, David Cantrell, David Dick, David Golden,
+David Mitchell, David M. Syzdek, David Nicol, David Wheeler, Dennis
+Kaarsemaker, Dintelmann, Peter, Dominic Dunlop, Dr.Ruud, Duke Leto,
+Enrico Sorcinelli, Eric Brine, Father Chrysostomos, Florian Ragwitz,
+Frank Wiegand, Gabor Szabo, Gene Sullivan, Geoffrey T. Dairiki, George
+Greer, Gerard Goossen, Gisle Aas, Goro Fuji, Graham Barr, Green, Paul,
+Hans Dieter Pearcey, Harmen, H. Merijn Brand, Hugo van der Sanden,
+Ian Goodacre, Igor Sutton, Ingo Weinhold, James Bence, James Mastros,
+Jan Dubois, Jari Aalto, Jarkko Hietaniemi, Jay Hannah, Jerry Hedden,
+Jesse Vincent, Jim Cromie, Jody Belka, John E. Malmberg, John Malmberg,
+John Peacock, John Peacock via RT, John P. Linderman, John Wright,
+Josh ben Jore, Jos I. Boumans, Karl Williamson, Kenichi Ishigaki, Ken
+Williams, Kevin Brintnall, Kevin Ryde, Kurt Starsinic, Leon Brocard,
+Lubomir Rintel, Luke Ross, Marcel Grünauer, Marcus Holland-Moritz, Mark
+Jason Dominus, Marko Asplund, Martin Hasch, Mashrab Kuvatov, Matt Kraai,
+Matt S Trout, Max Maischein, Michael Breen, Michael Cartmell, Michael
+G Schwern, Michael Witten, Mike Giroux, Milosz Tanski, Moritz Lenz,
+Nicholas Clark, Nick Cleaton, Niko Tyni, Offer Kaye, Osvaldo Villalon,
+Paul Fenwick, Paul Gaborit, Paul Green, Paul Johnson, Paul Marquess,
+Philip Hazel, Philippe Bruhat, Rafael Garcia-Suarez, Rainer Tammer,
+Rajesh Mandalemula, Reini Urban, Renée Bäcker, Ricardo Signes,
+Ricardo SIGNES, Richard Foley, Rich Rauenzahn, Rick Delaney, Risto
+Kankkunen, Robert May, Roberto C. Sanchez, Robin Barker, SADAHIRO
+Tomoyuki, Salvador Ortiz Garcia, Sam Vilain, Scott Lanning, Sébastien
+Aperghis-Tramoni, Sérgio Durigan Júnior, Shlomi Fish, Simon 'corecode'
+Schubert, Sisyphus, Slaven Rezic, Smylers, Steffen Müller, Steffen
+Ullrich, Stepan Kasal, Steve Hay, Steven Schubiger, Steve Peters, Tels,
+The Doctor, Tim Bunce, Tim Jenness, Todd Rinaldo, Tom Christiansen,
+Tom Hukins, Tom Wyant, Tony Cook, Torsten Schoenfeld, Tye McQueen,
+Vadim Konovalov, Vincent Pit, Hio YAMASHINA, Yasuhiro Matsumoto,
+Yitzchak Scott-Thoennes, Yuval Kogman, Yves Orton, Zefram, Zsban Ambrus
+
+This is woefully incomplete as it's automatically generated from version
+control history.  In particular, it doesn't include the names of the
+(very much appreciated) contributors who reported issues in previous
+versions of Perl that helped make Perl 5.12.0 better. For a more complete
+list of all of Perl's historical contributors, please see the C<AUTHORS>
+file in the Perl 5.12.0 distribution.
+
+Our "retired" pumpkings Nicholas Clark and Rafael Garcia-Suarez
+deserve special thanks for their brilliant and substantive ongoing
+contributions. Nicholas personally authored over 30% of the patches
+since 5.10.0. Rafael comes in second in patch authorship with 11%,
+but is first by a long shot in committing patches authored by others,
+pushing 44% of the commits since 5.10.0 in this category, often after
+providing considerable coaching to the patch authors. These statistics
+in no way comprise all of their contributions, but express in shorthand
+that we couldn't have done it without them.
+
+Many of the changes included in this version originated in the CPAN
+modules included in Perl's core. We're grateful to the entire CPAN
+community for helping Perl to flourish.
+
+=head1 Reporting Bugs
+
+If you find what you think is a bug, you might check the articles
+recently posted to the comp.lang.perl.misc newsgroup and the perl
+bug database at L<http://rt.perl.org/perlbug/>. There may also be
+information at L<http://www.perl.org/>, the Perl Home Page.
+
+If you believe you have an unreported bug, please run the B<perlbug>
+program included with your release. Be sure to trim your bug down
+to a tiny but sufficient test case. Your bug report, along with the
+output of C<perl -V>, will be sent off to perlbug@perl.org to be
+analyzed by the Perl porting team.
+
+If the bug you are reporting has security implications, which make it
+inappropriate to send to a publicly archived mailing list, then please send
+it to perl5-security-report@perl.org. This points to a closed subscription
+unarchived mailing list, which includes
+all the core committers, who will be able
+to help assess the impact of issues, figure out a resolution, and help
+co-ordinate the release of patches to mitigate or fix the problem across all
+platforms on which Perl is supported. Please only use this address for
+security issues in the Perl core, not for modules independently
+distributed on CPAN.
+
+=head1 SEE ALSO
+
+The F<Changes> file for an explanation of how to view exhaustive details
+on what changed.
+
+The F<INSTALL> file for how to build Perl.
+
+The F<README> file for general stuff.
 
-Many of the bug fixes in 5.12.0 were already seen in the 5.10.1
-maintenance release since the two releases were kept closely
-coordinated (while 5.12.0 was still called 5.11.something).
+The F<Artistic> and F<Copying> files for copyright information.
 
-You can see the list of changes in the 5.10.1 release 
-by reading L<perl5101delta>.
+L<http://dev.perl.org/perl5/errata.html> for a list of issues
+found after this release, as well as a list of CPAN modules known
+to be incompatible with this release.
 
+=cut