+=head2 Splitting the tokens C<(?> and C<(*> in regular expressions is
+now a fatal compilation error.
+
+These had been deprecated since v5.18.
+
+=head2 5 additional characters are treated as white space under C</x> in
+regex patterns (unless escaped)
+
+The use of these characters with C</x> outside bracketed character
+classes and when not preceeded by a backslash has raised a deprecation
+warning since v5.18. Now they will be ignored. See L</qrE<sol>fooE<sol>x>
+for the list of the five characters.
+
+=head2 Comment lines within S<C<(?[ ])>> now are ended only by a C<\n>
+
+S<C<(?[ ])>> is an experimental feature, introduced in v5.18. It operates
+as if C</x> is always enabled. But there was a difference, comment
+lines (following a C<#> character) were terminated by anything matching
+C<\R> which includes all vertical whitespace, such as form feeds. For
+consistency, this is now changed to match what terminates comment lines
+outside S<C<(?[ ])>>, namely a C<\n> (even if escaped), which is the
+same as what terminates a heredoc string and formats.
+
+=head2 Omitting % and @ on hash and array names is no longer permitted
+
+Really old Perl let you omit the @ on array names and the % on hash
+names in some spots. This has issued a deprecation warning since Perl
+5.0, and is no longer permitted.
+
+=head2 C<"$!"> text is now in English outside C<"use locale"> scope
+
+Previously, the text, unlike almost everything else, always came out
+based on the current underlying locale of the program. (Also affected
+on some systems is C<"$^E>".) For programs that are unprepared to
+handle locale, this can cause garbage text to be displayed. It's better
+to display text that is translatable via some tool than garbage text
+which is much harder to figure out.
+
+=head2 C<"$!"> text will be returned in UTF-8 when appropriate
+
+The stringification of C<$!> and C<$^E> will have the UTF-8 flag set
+when the text is actually non-ASCII UTF-8. This will enable programs
+that are set up to be locale-aware to properly output messages in the
+user's native language. Code that needs to continue the 5.20 and
+earlier behavior can do the stringification within the scopes of both
+'use bytes' and 'use locale ":messages". No other Perl operations will
+be affected by locale; only C<$!> and C<$^E> stringification. The
+'bytes' pragma causes the UTF-8 flag to not be set, just as in previous
+Perl releases. This resolves [perl #112208].
+
+=head2 MAD build option has been removed
+
+MAD = Misc Attribute Decoration; unmaintained attempt at preserving
+the Perl parse tree more faithfully so that automatic conversion of
+Perl 5 to Perl 6 would have been easier.
+
+This build-time configuration option had been unmaintained for years,
+and had probably seriously diverged on both Perl 5 and Perl 6 sides.
+