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+=head1 NAME
+
+perl5004delta - what's new for perl5.004
+
+=head1 DESCRIPTION
+
+This document describes differences between the 5.003 release (as
+documented in I<Programming Perl>, second edition--the Camel Book) and
+this one.
+
+=head1 Supported Environments
+
+Perl5.004 builds out of the box on Unix, Plan 9, LynxOS, VMS, OS/2,
+QNX, AmigaOS, and Windows NT.  Perl runs on Windows 95 as well, but it
+cannot be built there, for lack of a reasonable command interpreter.
+
+=head1 Core Changes
+
+Most importantly, many bugs were fixed, including several security
+problems.  See the F<Changes> file in the distribution for details.
+
+=head2 List assignment to %ENV works
+
+C<%ENV = ()> and C<%ENV = @list> now work as expected (except on VMS
+where it generates a fatal error).
+
+=head2 Change to "Can't locate Foo.pm in @INC" error
+
+The error "Can't locate Foo.pm in @INC" now lists the contents of @INC
+for easier debugging.
+
+=head2 Compilation option: Binary compatibility with 5.003
+
+There is a new Configure question that asks if you want to maintain
+binary compatibility with Perl 5.003.  If you choose binary
+compatibility, you do not have to recompile your extensions, but you
+might have symbol conflicts if you embed Perl in another application,
+just as in the 5.003 release.  By default, binary compatibility
+is preserved at the expense of symbol table pollution.
+
+=head2 $PERL5OPT environment variable
+
+You may now put Perl options in the $PERL5OPT environment variable.
+Unless Perl is running with taint checks, it will interpret this
+variable as if its contents had appeared on a "#!perl" line at the
+beginning of your script, except that hyphens are optional.  PERL5OPT
+may only be used to set the following switches: B<-[DIMUdmw]>.
+
+=head2 Limitations on B<-M>, B<-m>, and B<-T> options
+
+The C<-M> and C<-m> options are no longer allowed on the C<#!> line of
+a script.  If a script needs a module, it should invoke it with the
+C<use> pragma.
+
+The B<-T> option is also forbidden on the C<#!> line of a script,
+unless it was present on the Perl command line.  Due to the way C<#!>
+works, this usually means that B<-T> must be in the first argument.
+Thus:
+
+    #!/usr/bin/perl -T -w
+
+will probably work for an executable script invoked as C<scriptname>,
+while:
+
+    #!/usr/bin/perl -w -T
+
+will probably fail under the same conditions.  (Non-Unix systems will
+probably not follow this rule.)  But C<perl scriptname> is guaranteed
+to fail, since then there is no chance of B<-T> being found on the
+command line before it is found on the C<#!> line.
+
+=head2 More precise warnings
+
+If you removed the B<-w> option from your Perl 5.003 scripts because it
+made Perl too verbose, we recommend that you try putting it back when
+you upgrade to Perl 5.004.  Each new perl version tends to remove some
+undesirable warnings, while adding new warnings that may catch bugs in
+your scripts.
+
+=head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
+
+Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
+(using the C<@ISA> hierarchy), even when the function to be autoloaded
+was called as a plain function (e.g. C<Foo::bar()>), not a method
+(e.g. C<< Foo->bar() >> or C<< $obj->bar() >>).
+
+Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s.
+However, there is a significant base of existing code that may be using
+the old behavior.  So, as an interim step, Perl 5.004 issues an optional
+warning when a non-method uses an inherited C<AUTOLOAD>.
+
+The simple rule is:  Inheritance will not work when autoloading
+non-methods.  The simple fix for old code is:  In any module that used to
+depend on inheriting C<AUTOLOAD> for non-methods from a base class named
+C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup.
+
+=head2 Previously deprecated %OVERLOAD is no longer usable
+
+Using %OVERLOAD to define overloading was deprecated in 5.003.
+Overloading is now defined using the overload pragma. %OVERLOAD is
+still used internally but should not be used by Perl scripts. See
+L<overload> for more details.
+
+=head2 Subroutine arguments created only when they're modified
+
+In Perl 5.004, nonexistent array and hash elements used as subroutine
+parameters are brought into existence only if they are actually
+assigned to (via C<@_>).
+
+Earlier versions of Perl vary in their handling of such arguments.
+Perl versions 5.002 and 5.003 always brought them into existence.
+Perl versions 5.000 and 5.001 brought them into existence only if
+they were not the first argument (which was almost certainly a bug).
+Earlier versions of Perl never brought them into existence.
+
+For example, given this code:
+
+     undef @a; undef %a;
+     sub show { print $_[0] };
+     sub change { $_[0]++ };
+     show($a[2]);
+     change($a{b});
+
+After this code executes in Perl 5.004, $a{b} exists but $a[2] does
+not.  In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
+(but $a[2]'s value would have been undefined).
+
+=head2 Group vector changeable with C<$)>
+
+The C<$)> special variable has always (well, in Perl 5, at least)
+reflected not only the current effective group, but also the group list
+as returned by the C<getgroups()> C function (if there is one).
+However, until this release, there has not been a way to call the
+C<setgroups()> C function from Perl.
+
+In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining
+it: The first number in its string value is used as the effective gid;
+if there are any numbers after the first one, they are passed to the
+C<setgroups()> C function (if there is one).
+
+=head2 Fixed parsing of $$<digit>, &$<digit>, etc.
+
+Perl versions before 5.004 misinterpreted any type marker followed by
+"$" and a digit.  For example, "$$0" was incorrectly taken to mean
+"${$}0" instead of "${$0}".  This bug is (mostly) fixed in Perl 5.004.
+
+However, the developers of Perl 5.004 could not fix this bug completely,
+because at least two widely-used modules depend on the old meaning of
+"$$0" in a string.  So Perl 5.004 still interprets "$$<digit>" in the
+old (broken) way inside strings; but it generates this message as a
+warning.  And in Perl 5.005, this special treatment will cease.
+
+=head2 Fixed localization of $<digit>, $&, etc.
+
+Perl versions before 5.004 did not always properly localize the
+regex-related special variables.  Perl 5.004 does localize them, as
+the documentation has always said it should.  This may result in $1,
+$2, etc. no longer being set where existing programs use them.
+
+=head2 No resetting of $. on implicit close
+
+The documentation for Perl 5.0 has always stated that C<$.> is I<not>
+reset when an already-open file handle is reopened with no intervening
+call to C<close>.  Due to a bug, perl versions 5.000 through 5.003
+I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
+
+=head2 C<wantarray> may return undef
+
+The C<wantarray> operator returns true if a subroutine is expected to
+return a list, and false otherwise.  In Perl 5.004, C<wantarray> can
+also return the undefined value if a subroutine's return value will
+not be used at all, which allows subroutines to avoid a time-consuming
+calculation of a return value if it isn't going to be used.
+
+=head2 C<eval EXPR> determines value of EXPR in scalar context
+
+Perl (version 5) used to determine the value of EXPR inconsistently,
+sometimes incorrectly using the surrounding context for the determination.
+Now, the value of EXPR (before being parsed by eval) is always determined in
+a scalar context.  Once parsed, it is executed as before, by providing
+the context that the scope surrounding the eval provided.  This change
+makes the behavior Perl4 compatible, besides fixing bugs resulting from
+the inconsistent behavior.  This program:
+
+    @a = qw(time now is time);
+    print eval @a;
+    print '|', scalar eval @a;
+
+used to print something like "timenowis881399109|4", but now (and in perl4)
+prints "4|4".
+
+=head2 Changes to tainting checks
+
+A bug in previous versions may have failed to detect some insecure
+conditions when taint checks are turned on.  (Taint checks are used
+in setuid or setgid scripts, or when explicitly turned on with the
+C<-T> invocation option.)  Although it's unlikely, this may cause a
+previously-working script to now fail -- which should be construed
+as a blessing, since that indicates a potentially-serious security
+hole was just plugged.
+
+The new restrictions when tainting include:
+
+=over 4
+
+=item No glob() or <*>
+
+These operators may spawn the C shell (csh), which cannot be made
+safe.  This restriction will be lifted in a future version of Perl
+when globbing is implemented without the use of an external program.
+
+=item No spawning if tainted $CDPATH, $ENV, $BASH_ENV
+
+These environment variables may alter the behavior of spawned programs
+(especially shells) in ways that subvert security.  So now they are
+treated as dangerous, in the manner of $IFS and $PATH.
+
+=item No spawning if tainted $TERM doesn't look like a terminal name
+
+Some termcap libraries do unsafe things with $TERM.  However, it would be
+unnecessarily harsh to treat all $TERM values as unsafe, since only shell
+metacharacters can cause trouble in $TERM.  So a tainted $TERM is
+considered to be safe if it contains only alphanumerics, underscores,
+dashes, and colons, and unsafe if it contains other characters (including
+whitespace).
+
+=back
+
+=head2 New Opcode module and revised Safe module
+
+A new Opcode module supports the creation, manipulation and
+application of opcode masks.  The revised Safe module has a new API
+and is implemented using the new Opcode module.  Please read the new
+Opcode and Safe documentation.
+
+=head2 Embedding improvements
+
+In older versions of Perl it was not possible to create more than one
+Perl interpreter instance inside a single process without leaking like a
+sieve and/or crashing.  The bugs that caused this behavior have all been
+fixed.  However, you still must take care when embedding Perl in a C
+program.  See the updated perlembed manpage for tips on how to manage
+your interpreters.
+
+=head2 Internal change: FileHandle class based on IO::* classes
+
+File handles are now stored internally as type IO::Handle.  The
+FileHandle module is still supported for backwards compatibility, but
+it is now merely a front end to the IO::* modules -- specifically,
+IO::Handle, IO::Seekable, and IO::File.  We suggest, but do not
+require, that you use the IO::* modules in new code.
+
+In harmony with this change, C<*GLOB{FILEHANDLE}> is now just a
+backward-compatible synonym for C<*GLOB{IO}>.
+
+=head2 Internal change: PerlIO abstraction interface
+
+It is now possible to build Perl with AT&T's sfio IO package
+instead of stdio.  See L<perlapio> for more details, and
+the F<INSTALL> file for how to use it.
+
+=head2 New and changed syntax
+
+=over 4
+
+=item $coderef->(PARAMS)
+
+A subroutine reference may now be suffixed with an arrow and a
+(possibly empty) parameter list.  This syntax denotes a call of the
+referenced subroutine, with the given parameters (if any).
+
+This new syntax follows the pattern of S<C<< $hashref->{FOO} >>> and
+S<C<< $aryref->[$foo] >>>: You may now write S<C<&$subref($foo)>> as
+S<C<< $subref->($foo) >>>.  All these arrow terms may be chained;
+thus, S<C<< &{$table->{FOO}}($bar) >>> may now be written
+S<C<< $table->{FOO}->($bar) >>>.
+
+=back
+
+=head2 New and changed builtin constants
+
+=over 4
+
+=item __PACKAGE__
+
+The current package name at compile time, or the undefined value if
+there is no current package (due to a C<package;> directive).  Like
+C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate
+into strings.
+
+=back
+
+=head2 New and changed builtin variables
+
+=over 4
+
+=item $^E
+
+Extended error message on some platforms.  (Also known as
+$EXTENDED_OS_ERROR if you C<use English>).
+
+=item $^H
+
+The current set of syntax checks enabled by C<use strict>.  See the
+documentation of C<strict> for more details.  Not actually new, but
+newly documented.
+Because it is intended for internal use by Perl core components,
+there is no C<use English> long name for this variable.
+
+=item $^M
+
+By default, running out of memory it is not trappable.  However, if
+compiled for this, Perl may use the contents of C<$^M> as an emergency
+pool after die()ing with this message.  Suppose that your Perl were
+compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc.  Then
+
+    $^M = 'a' x (1<<16);
+
+would allocate a 64K buffer for use when in emergency.
+See the F<INSTALL> file for information on how to enable this option.
+As a disincentive to casual use of this advanced feature,
+there is no C<use English> long name for this variable.
+
+=back
+
+=head2 New and changed builtin functions
+
+=over 4
+
+=item delete on slices
+
+This now works.  (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
+
+=item flock
+
+is now supported on more platforms, prefers fcntl to lockf when
+emulating, and always flushes before (un)locking.
+
+=item printf and sprintf
+
+Perl now implements these functions itself; it doesn't use the C
+library function sprintf() any more, except for floating-point
+numbers, and even then only known flags are allowed.  As a result, it
+is now possible to know which conversions and flags will work, and
+what they will do.
+
+The new conversions in Perl's sprintf() are:
+
+   %i	a synonym for %d
+   %p	a pointer (the address of the Perl value, in hexadecimal)
+   %n	special: *stores* the number of characters output so far
+        into the next variable in the parameter list 
+
+The new flags that go between the C<%> and the conversion are:
+
+   #	prefix octal with "0", hex with "0x"
+   h	interpret integer as C type "short" or "unsigned short"
+   V	interpret integer as Perl's standard integer type
+
+Also, where a number would appear in the flags, an asterisk ("*") may
+be used instead, in which case Perl uses the next item in the
+parameter list as the given number (that is, as the field width or
+precision).  If a field width obtained through "*" is negative, it has
+the same effect as the '-' flag: left-justification.
+
+See L<perlfunc/sprintf> for a complete list of conversion and flags.
+
+=item keys as an lvalue
+
+As an lvalue, C<keys> allows you to increase the number of hash buckets
+allocated for the given hash.  This can gain you a measure of efficiency if
+you know the hash is going to get big.  (This is similar to pre-extending
+an array by assigning a larger number to $#array.)  If you say
+
+    keys %hash = 200;
+
+then C<%hash> will have at least 200 buckets allocated for it.  These
+buckets will be retained even if you do C<%hash = ()>; use C<undef
+%hash> if you want to free the storage while C<%hash> is still in scope.
+You can't shrink the number of buckets allocated for the hash using
+C<keys> in this way (but you needn't worry about doing this by accident,
+as trying has no effect).
+
+=item my() in Control Structures
+
+You can now use my() (with or without the parentheses) in the control
+expressions of control structures such as:
+
+    while (defined(my $line = <>)) {
+        $line = lc $line;
+    } continue {
+        print $line;
+    }
+
+    if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
+        user_agrees();
+    } elsif ($answer =~ /^n(o)?$/i) {
+        user_disagrees();
+    } else {
+        chomp $answer;
+        die "`$answer' is neither `yes' nor `no'";
+    }
+
+Also, you can declare a foreach loop control variable as lexical by
+preceding it with the word "my".  For example, in:
+
+    foreach my $i (1, 2, 3) {
+        some_function();
+    }
+
+$i is a lexical variable, and the scope of $i extends to the end of
+the loop, but not beyond it.
+
+Note that you still cannot use my() on global punctuation variables
+such as $_ and the like.
+
+=item pack() and unpack()
+
+A new format 'w' represents a BER compressed integer (as defined in
+ASN.1).  Its format is a sequence of one or more bytes, each of which
+provides seven bits of the total value, with the most significant
+first.  Bit eight of each byte is set, except for the last byte, in
+which bit eight is clear.
+
+If 'p' or 'P' are given undef as values, they now generate a NULL
+pointer.
+
+Both pack() and unpack() now fail when their templates contain invalid
+types.  (Invalid types used to be ignored.)
+
+=item sysseek()
+
+The new sysseek() operator is a variant of seek() that sets and gets the
+file's system read/write position, using the lseek(2) system call.  It is
+the only reliable way to seek before using sysread() or syswrite().  Its
+return value is the new position, or the undefined value on failure.
+
+=item use VERSION
+
+If the first argument to C<use> is a number, it is treated as a version
+number instead of a module name.  If the version of the Perl interpreter
+is less than VERSION, then an error message is printed and Perl exits
+immediately.  Because C<use> occurs at compile time, this check happens
+immediately during the compilation process, unlike C<require VERSION>,
+which waits until runtime for the check.  This is often useful if you
+need to check the current Perl version before C<use>ing library modules
+which have changed in incompatible ways from older versions of Perl.
+(We try not to do this more than we have to.)
+
+=item use Module VERSION LIST
+
+If the VERSION argument is present between Module and LIST, then the
+C<use> will call the VERSION method in class Module with the given
+version as an argument.  The default VERSION method, inherited from
+the UNIVERSAL class, croaks if the given version is larger than the
+value of the variable $Module::VERSION.  (Note that there is not a
+comma after VERSION!)
+
+This version-checking mechanism is similar to the one currently used
+in the Exporter module, but it is faster and can be used with modules
+that don't use the Exporter.  It is the recommended method for new
+code.
+
+=item prototype(FUNCTION)
+
+Returns the prototype of a function as a string (or C<undef> if the
+function has no prototype).  FUNCTION is a reference to or the name of the
+function whose prototype you want to retrieve.
+(Not actually new; just never documented before.)
+
+=item srand
+
+The default seed for C<srand>, which used to be C<time>, has been changed.
+Now it's a heady mix of difficult-to-predict system-dependent values,
+which should be sufficient for most everyday purposes.
+
+Previous to version 5.004, calling C<rand> without first calling C<srand>
+would yield the same sequence of random numbers on most or all machines.
+Now, when perl sees that you're calling C<rand> and haven't yet called
+C<srand>, it calls C<srand> with the default seed. You should still call
+C<srand> manually if your code might ever be run on a pre-5.004 system,
+of course, or if you want a seed other than the default.
+
+=item $_ as Default
+
+Functions documented in the Camel to default to $_ now in
+fact do, and all those that do are so documented in L<perlfunc>.
+
+=item C<m//gc> does not reset search position on failure
+
+The C<m//g> match iteration construct has always reset its target
+string's search position (which is visible through the C<pos> operator)
+when a match fails; as a result, the next C<m//g> match after a failure
+starts again at the beginning of the string.  With Perl 5.004, this
+reset may be disabled by adding the "c" (for "continue") modifier,
+i.e. C<m//gc>.  This feature, in conjunction with the C<\G> zero-width
+assertion, makes it possible to chain matches together.  See L<perlop>
+and L<perlre>.
+
+=item C<m//x> ignores whitespace before ?*+{}
+
+The C<m//x> construct has always been intended to ignore all unescaped
+whitespace.  However, before Perl 5.004, whitespace had the effect of
+escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
+(mis)interpreted as C</a\*b/x>.  This bug has been fixed in 5.004.
+
+=item nested C<sub{}> closures work now
+
+Prior to the 5.004 release, nested anonymous functions didn't work
+right.  They do now.
+
+=item formats work right on changing lexicals
+
+Just like anonymous functions that contain lexical variables
+that change (like a lexical index variable for a C<foreach> loop),
+formats now work properly.  For example, this silently failed
+before (printed only zeros), but is fine now:
+
+    my $i;
+    foreach $i ( 1 .. 10 ) {
+	write;
+    }
+    format =
+	my i is @#
+	$i
+    .
+
+However, it still fails (without a warning) if the foreach is within a
+subroutine:
+
+    my $i;
+    sub foo {
+      foreach $i ( 1 .. 10 ) {
+	write;
+      }
+    }
+    foo;
+    format =
+	my i is @#
+	$i
+    .
+
+=back
+
+=head2 New builtin methods
+
+The C<UNIVERSAL> package automatically contains the following methods that
+are inherited by all other classes:
+
+=over 4
+
+=item isa(CLASS)
+
+C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
+
+C<isa> is also exportable and can be called as a sub with two arguments. This
+allows the ability to check what a reference points to. Example:
+
+    use UNIVERSAL qw(isa);
+
+    if(isa($ref, 'ARRAY')) {
+       ...
+    }
+
+=item can(METHOD)
+
+C<can> checks to see if its object has a method called C<METHOD>,
+if it does then a reference to the sub is returned; if it does not then
+I<undef> is returned.
+
+=item VERSION( [NEED] )
+
+C<VERSION> returns the version number of the class (package).  If the
+NEED argument is given then it will check that the current version (as
+defined by the $VERSION variable in the given package) not less than
+NEED; it will die if this is not the case.  This method is normally
+called as a class method.  This method is called automatically by the
+C<VERSION> form of C<use>.
+
+    use A 1.2 qw(some imported subs);
+    # implies:
+    A->VERSION(1.2);
+
+=back
+
+B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
+C<isa> uses a very similar method and caching strategy. This may cause
+strange effects if the Perl code dynamically changes @ISA in any package.
+
+You may add other methods to the UNIVERSAL class via Perl or XS code.
+You do not need to C<use UNIVERSAL> in order to make these methods
+available to your program.  This is necessary only if you wish to
+have C<isa> available as a plain subroutine in the current package.
+
+=head2 TIEHANDLE now supported
+
+See L<perltie> for other kinds of tie()s.
+
+=over 4
+
+=item TIEHANDLE classname, LIST
+
+This is the constructor for the class.  That means it is expected to
+return an object of some sort. The reference can be used to
+hold some internal information.
+
+    sub TIEHANDLE {
+	print "<shout>\n";
+	my $i;
+	return bless \$i, shift;
+    }
+
+=item PRINT this, LIST
+
+This method will be triggered every time the tied handle is printed to.
+Beyond its self reference it also expects the list that was passed to
+the print function.
+
+    sub PRINT {
+	$r = shift;
+	$$r++;
+	return print join( $, => map {uc} @_), $\;
+    }
+
+=item PRINTF this, LIST
+
+This method will be triggered every time the tied handle is printed to
+with the C<printf()> function.
+Beyond its self reference it also expects the format and list that was
+passed to the printf function.
+
+    sub PRINTF {
+        shift;
+	  my $fmt = shift;
+        print sprintf($fmt, @_)."\n";
+    }
+
+=item READ this LIST
+
+This method will be called when the handle is read from via the C<read>
+or C<sysread> functions.
+
+    sub READ {
+	$r = shift;
+	my($buf,$len,$offset) = @_;
+	print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
+    }
+
+=item READLINE this
+
+This method will be called when the handle is read from. The method
+should return undef when there is no more data.
+
+    sub READLINE {
+	$r = shift;
+	return "PRINT called $$r times\n"
+    }
+
+=item GETC this
+
+This method will be called when the C<getc> function is called.
+
+    sub GETC { print "Don't GETC, Get Perl"; return "a"; }
+
+=item DESTROY this
+
+As with the other types of ties, this method will be called when the
+tied handle is about to be destroyed. This is useful for debugging and
+possibly for cleaning up.
+
+    sub DESTROY {
+	print "</shout>\n";
+    }
+
+=back
+
+=head2 Malloc enhancements
+
+If perl is compiled with the malloc included with the perl distribution
+(that is, if C<perl -V:d_mymalloc> is 'define') then you can print
+memory statistics at runtime by running Perl thusly:
+
+  env PERL_DEBUG_MSTATS=2 perl your_script_here
+
+The value of 2 means to print statistics after compilation and on
+exit; with a value of 1, the statistics are printed only on exit.
+(If you want the statistics at an arbitrary time, you'll need to
+install the optional module Devel::Peek.)
+
+Three new compilation flags are recognized by malloc.c.  (They have no
+effect if perl is compiled with system malloc().)
+
+=over 4
+
+=item -DPERL_EMERGENCY_SBRK
+
+If this macro is defined, running out of memory need not be a fatal
+error: a memory pool can allocated by assigning to the special
+variable C<$^M>.  See L<"$^M">.
+
+=item -DPACK_MALLOC
+
+Perl memory allocation is by bucket with sizes close to powers of two.
+Because of these malloc overhead may be big, especially for data of
+size exactly a power of two.  If C<PACK_MALLOC> is defined, perl uses
+a slightly different algorithm for small allocations (up to 64 bytes
+long), which makes it possible to have overhead down to 1 byte for
+allocations which are powers of two (and appear quite often).
+
+Expected memory savings (with 8-byte alignment in C<alignbytes>) is
+about 20% for typical Perl usage.  Expected slowdown due to additional
+malloc overhead is in fractions of a percent (hard to measure, because
+of the effect of saved memory on speed).
+
+=item -DTWO_POT_OPTIMIZE
+
+Similarly to C<PACK_MALLOC>, this macro improves allocations of data
+with size close to a power of two; but this works for big allocations
+(starting with 16K by default).  Such allocations are typical for big
+hashes and special-purpose scripts, especially image processing.
+
+On recent systems, the fact that perl requires 2M from system for 1M
+allocation will not affect speed of execution, since the tail of such
+a chunk is not going to be touched (and thus will not require real
+memory).  However, it may result in a premature out-of-memory error.
+So if you will be manipulating very large blocks with sizes close to
+powers of two, it would be wise to define this macro.
+
+Expected saving of memory is 0-100% (100% in applications which
+require most memory in such 2**n chunks); expected slowdown is
+negligible.
+
+=back
+
+=head2 Miscellaneous efficiency enhancements
+
+Functions that have an empty prototype and that do nothing but return
+a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
+
+Each unique hash key is only allocated once, no matter how many hashes
+have an entry with that key.  So even if you have 100 copies of the
+same hash, the hash keys never have to be reallocated.
+
+=head1 Support for More Operating Systems
+
+Support for the following operating systems is new in Perl 5.004.
+
+=head2 Win32
+
+Perl 5.004 now includes support for building a "native" perl under
+Windows NT, using the Microsoft Visual C++ compiler (versions 2.0
+and above) or the Borland C++ compiler (versions 5.02 and above).
+The resulting perl can be used under Windows 95 (if it
+is installed in the same directory locations as it got installed
+in Windows NT).  This port includes support for perl extension
+building tools like L<MakeMaker> and L<h2xs>, so that many extensions
+available on the Comprehensive Perl Archive Network (CPAN) can now be
+readily built under Windows NT.  See http://www.perl.com/ for more
+information on CPAN and F<README.win32> in the perl distribution for more
+details on how to get started with building this port.
+
+There is also support for building perl under the Cygwin32 environment.
+Cygwin32 is a set of GNU tools that make it possible to compile and run
+many Unix programs under Windows NT by providing a mostly Unix-like 
+interface for compilation and execution.  See F<README.cygwin32> in the
+perl distribution for more details on this port and how to obtain the
+Cygwin32 toolkit.
+
+=head2 Plan 9
+
+See F<README.plan9> in the perl distribution.
+
+=head2 QNX
+
+See F<README.qnx> in the perl distribution.
+
+=head2 AmigaOS
+
+See F<README.amigaos> in the perl distribution.
+
+=head1 Pragmata
+
+Six new pragmatic modules exist:
+
+=over 4
+
+=item use autouse MODULE => qw(sub1 sub2 sub3)
+
+Defers C<require MODULE> until someone calls one of the specified
+subroutines (which must be exported by MODULE).  This pragma should be
+used with caution, and only when necessary.
+
+=item use blib
+
+=item use blib 'dir'
+
+Looks for MakeMaker-like I<'blib'> directory structure starting in
+I<dir> (or current directory) and working back up to five levels of
+parent directories.
+
+Intended for use on command line with B<-M> option as a way of testing
+arbitrary scripts against an uninstalled version of a package.
+
+=item use constant NAME => VALUE
+
+Provides a convenient interface for creating compile-time constants,
+See L<perlsub/"Constant Functions">.
+
+=item use locale
+
+Tells the compiler to enable (or disable) the use of POSIX locales for
+builtin operations.
+
+When C<use locale> is in effect, the current LC_CTYPE locale is used
+for regular expressions and case mapping; LC_COLLATE for string
+ordering; and LC_NUMERIC for numeric formatting in printf and sprintf
+(but B<not> in print).  LC_NUMERIC is always used in write, since
+lexical scoping of formats is problematic at best.
+
+Each C<use locale> or C<no locale> affects statements to the end of
+the enclosing BLOCK or, if not inside a BLOCK, to the end of the
+current file.  Locales can be switched and queried with
+POSIX::setlocale().
+
+See L<perllocale> for more information.
+
+=item use ops
+
+Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
+
+=item use vmsish
+
+Enable VMS-specific language features.  Currently, there are three
+VMS-specific features available: 'status', which makes C<$?> and
+C<system> return genuine VMS status values instead of emulating POSIX;
+'exit', which makes C<exit> take a genuine VMS status value instead of
+assuming that C<exit 1> is an error; and 'time', which makes all times
+relative to the local time zone, in the VMS tradition.
+
+=back
+
+=head1 Modules
+
+=head2 Required Updates
+
+Though Perl 5.004 is compatible with almost all modules that work
+with Perl 5.003, there are a few exceptions:
+
+    Module   Required Version for Perl 5.004
+    ------   -------------------------------
+    Filter   Filter-1.12
+    LWP      libwww-perl-5.08
+    Tk       Tk400.202 (-w makes noise)
+
+Also, the majordomo mailing list program, version 1.94.1, doesn't work
+with Perl 5.004 (nor with perl 4), because it executes an invalid
+regular expression.  This bug is fixed in majordomo version 1.94.2.
+
+=head2 Installation directories
+
+The I<installperl> script now places the Perl source files for
+extensions in the architecture-specific library directory, which is
+where the shared libraries for extensions have always been.  This
+change is intended to allow administrators to keep the Perl 5.004
+library directory unchanged from a previous version, without running
+the risk of binary incompatibility between extensions' Perl source and
+shared libraries.
+
+=head2 Module information summary
+
+Brand new modules, arranged by topic rather than strictly
+alphabetically:
+
+    CGI.pm               Web server interface ("Common Gateway Interface")
+    CGI/Apache.pm        Support for Apache's Perl module
+    CGI/Carp.pm          Log server errors with helpful context
+    CGI/Fast.pm          Support for FastCGI (persistent server process)
+    CGI/Push.pm          Support for server push
+    CGI/Switch.pm        Simple interface for multiple server types
+
+    CPAN                 Interface to Comprehensive Perl Archive Network
+    CPAN::FirstTime      Utility for creating CPAN configuration file
+    CPAN::Nox            Runs CPAN while avoiding compiled extensions
+
+    IO.pm                Top-level interface to IO::* classes
+    IO/File.pm           IO::File extension Perl module
+    IO/Handle.pm         IO::Handle extension Perl module
+    IO/Pipe.pm           IO::Pipe extension Perl module
+    IO/Seekable.pm       IO::Seekable extension Perl module
+    IO/Select.pm         IO::Select extension Perl module
+    IO/Socket.pm         IO::Socket extension Perl module
+
+    Opcode.pm            Disable named opcodes when compiling Perl code
+
+    ExtUtils/Embed.pm    Utilities for embedding Perl in C programs
+    ExtUtils/testlib.pm  Fixes up @INC to use just-built extension
+
+    FindBin.pm           Find path of currently executing program
+
+    Class/Struct.pm      Declare struct-like datatypes as Perl classes
+    File/stat.pm         By-name interface to Perl's builtin stat
+    Net/hostent.pm       By-name interface to Perl's builtin gethost*
+    Net/netent.pm        By-name interface to Perl's builtin getnet*
+    Net/protoent.pm      By-name interface to Perl's builtin getproto*
+    Net/servent.pm       By-name interface to Perl's builtin getserv*
+    Time/gmtime.pm       By-name interface to Perl's builtin gmtime
+    Time/localtime.pm    By-name interface to Perl's builtin localtime
+    Time/tm.pm           Internal object for Time::{gm,local}time
+    User/grent.pm        By-name interface to Perl's builtin getgr*
+    User/pwent.pm        By-name interface to Perl's builtin getpw*
+
+    Tie/RefHash.pm       Base class for tied hashes with references as keys
+
+    UNIVERSAL.pm         Base class for *ALL* classes
+
+=head2 Fcntl
+
+New constants in the existing Fcntl modules are now supported,
+provided that your operating system happens to support them:
+
+    F_GETOWN F_SETOWN
+    O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
+    O_EXLOCK O_SHLOCK
+
+These constants are intended for use with the Perl operators sysopen()
+and fcntl() and the basic database modules like SDBM_File.  For the
+exact meaning of these and other Fcntl constants please refer to your
+operating system's documentation for fcntl() and open().
+
+In addition, the Fcntl module now provides these constants for use
+with the Perl operator flock():
+
+	LOCK_SH LOCK_EX LOCK_NB LOCK_UN
+
+These constants are defined in all environments (because where there is
+no flock() system call, Perl emulates it).  However, for historical
+reasons, these constants are not exported unless they are explicitly
+requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
+
+=head2 IO
+
+The IO module provides a simple mechanism to load all the IO modules at one
+go.  Currently this includes:
+
+     IO::Handle
+     IO::Seekable
+     IO::File
+     IO::Pipe
+     IO::Socket
+
+For more information on any of these modules, please see its
+respective documentation.
+
+=head2 Math::Complex
+
+The Math::Complex module has been totally rewritten, and now supports
+more operations.  These are overloaded:
+
+     + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
+
+And these functions are now exported:
+
+    pi i Re Im arg
+    log10 logn ln cbrt root
+    tan
+    csc sec cot
+    asin acos atan
+    acsc asec acot
+    sinh cosh tanh
+    csch sech coth
+    asinh acosh atanh
+    acsch asech acoth
+    cplx cplxe
+
+=head2 Math::Trig
+
+This new module provides a simpler interface to parts of Math::Complex for
+those who need trigonometric functions only for real numbers.
+
+=head2 DB_File
+
+There have been quite a few changes made to DB_File. Here are a few of
+the highlights:
+
+=over 4
+
+=item *
+
+Fixed a handful of bugs.
+
+=item *
+
+By public demand, added support for the standard hash function exists().
+
+=item *
+
+Made it compatible with Berkeley DB 1.86.
+
+=item *
+
+Made negative subscripts work with RECNO interface.
+
+=item *
+
+Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
+mode from 0640 to 0666.
+
+=item *
+
+Made DB_File automatically import the open() constants (O_RDWR,
+O_CREAT etc.) from Fcntl, if available.
+
+=item *
+
+Updated documentation.
+
+=back
+
+Refer to the HISTORY section in DB_File.pm for a complete list of
+changes. Everything after DB_File 1.01 has been added since 5.003.
+
+=head2 Net::Ping
+
+Major rewrite - support added for both udp echo and real icmp pings.
+
+=head2 Object-oriented overrides for builtin operators
+
+Many of the Perl builtins returning lists now have
+object-oriented overrides.  These are:
+
+    File::stat
+    Net::hostent
+    Net::netent
+    Net::protoent
+    Net::servent
+    Time::gmtime
+    Time::localtime
+    User::grent
+    User::pwent
+
+For example, you can now say
+
+    use File::stat;
+    use User::pwent;
+    $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
+
+=head1 Utility Changes
+
+=head2 pod2html
+
+=over 4
+
+=item Sends converted HTML to standard output
+
+The I<pod2html> utility included with Perl 5.004 is entirely new.
+By default, it sends the converted HTML to its standard output,
+instead of writing it to a file like Perl 5.003's I<pod2html> did.
+Use the B<--outfile=FILENAME> option to write to a file.
+
+=back
+
+=head2 xsubpp
+
+=over 4
+
+=item C<void> XSUBs now default to returning nothing
+
+Due to a documentation/implementation bug in previous versions of
+Perl, XSUBs with a return type of C<void> have actually been
+returning one value.  Usually that value was the GV for the XSUB,
+but sometimes it was some already freed or reused value, which would
+sometimes lead to program failure.
+
+In Perl 5.004, if an XSUB is declared as returning C<void>, it
+actually returns no value, i.e. an empty list (though there is a
+backward-compatibility exception; see below).  If your XSUB really
+does return an SV, you should give it a return type of C<SV *>.
+
+For backward compatibility, I<xsubpp> tries to guess whether a
+C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
+It does so by examining the text of the XSUB: if I<xsubpp> finds
+what looks like an assignment to C<ST(0)>, it assumes that the
+XSUB's return type is really C<SV *>.
+
+=back
+
+=head1 C Language API Changes
+
+=over 4
+
+=item C<gv_fetchmethod> and C<perl_call_sv>
+
+The C<gv_fetchmethod> function finds a method for an object, just like
+in Perl 5.003.  The GV it returns may be a method cache entry.
+However, in Perl 5.004, method cache entries are not visible to users;
+therefore, they can no longer be passed directly to C<perl_call_sv>.
+Instead, you should use the C<GvCV> macro on the GV to extract its CV,
+and pass the CV to C<perl_call_sv>.
+
+The most likely symptom of passing the result of C<gv_fetchmethod> to
+C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
+error on the I<second> call to a given method (since there is no cache
+on the first call).
+
+=item C<perl_eval_pv>
+
+A new function handy for eval'ing strings of Perl code inside C code.
+This function returns the value from the eval statement, which can
+be used instead of fetching globals from the symbol table.  See
+L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
+
+=item Extended API for manipulating hashes
+
+Internal handling of hash keys has changed.  The old hashtable API is
+still fully supported, and will likely remain so.  The additions to the
+API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
+real scalars as keys rather than plain strings (nontied hashes still
+can only use strings as keys).  New extensions must use the new hash
+access functions and macros if they wish to use C<SV*> keys.  These
+additions also make it feasible to manipulate C<HE*>s (hash entries),
+which can be more efficient.  See L<perlguts> for details.
+
+=back
+
+=head1 Documentation Changes
+
+Many of the base and library pods were updated.  These
+new pods are included in section 1:
+
+=over 4
+
+=item L<perldelta>
+
+This document.
+
+=item L<perlfaq>
+
+Frequently asked questions.
+
+=item L<perllocale>
+
+Locale support (internationalization and localization).
+
+=item L<perltoot>
+
+Tutorial on Perl OO programming.
+
+=item L<perlapio>
+
+Perl internal IO abstraction interface.
+
+=item L<perlmodlib>
+
+Perl module library and recommended practice for module creation.
+Extracted from L<perlmod> (which is much smaller as a result).
+
+=item L<perldebug>
+
+Although not new, this has been massively updated.
+
+=item L<perlsec>
+
+Although not new, this has been massively updated.
+
+=back
+
+=head1 New Diagnostics
+
+Several new conditions will trigger warnings that were
+silent before.  Some only affect certain platforms.
+The following new warnings and errors outline these.
+These messages are classified as follows (listed in
+increasing order of desperation):
+
+   (W) A warning (optional).
+   (D) A deprecation (optional).
+   (S) A severe warning (mandatory).
+   (F) A fatal error (trappable).
+   (P) An internal error you should never see (trappable).
+   (X) A very fatal error (nontrappable).
+   (A) An alien error message (not generated by Perl).
+
+=over 4
+
+=item "my" variable %s masks earlier declaration in same scope
+
+(W) A lexical variable has been redeclared in the same scope, effectively
+eliminating all access to the previous instance.  This is almost always
+a typographical error.  Note that the earlier variable will still exist
+until the end of the scope or until all closure referents to it are
+destroyed.
+
+=item %s argument is not a HASH element or slice
+
+(F) The argument to delete() must be either a hash element, such as
+
+    $foo{$bar}
+    $ref->[12]->{"susie"}
+
+or a hash slice, such as
+
+    @foo{$bar, $baz, $xyzzy}
+    @{$ref->[12]}{"susie", "queue"}
+
+=item Allocation too large: %lx
+
+(X) You can't allocate more than 64K on an MS-DOS machine.
+
+=item Allocation too large
+
+(F) You can't allocate more than 2^31+"small amount" bytes.
+
+=item Applying %s to %s will act on scalar(%s)
+
+(W) The pattern match (//), substitution (s///), and transliteration (tr///)
+operators work on scalar values.  If you apply one of them to an array
+or a hash, it will convert the array or hash to a scalar value -- the
+length of an array, or the population info of a hash -- and then work on
+that scalar value.  This is probably not what you meant to do.  See
+L<perlfunc/grep> and L<perlfunc/map> for alternatives.
+
+=item Attempt to free nonexistent shared string
+
+(P) Perl maintains a reference counted internal table of strings to
+optimize the storage and access of hash keys and other strings.  This
+indicates someone tried to decrement the reference count of a string
+that can no longer be found in the table.
+
+=item Attempt to use reference as lvalue in substr
+
+(W) You supplied a reference as the first argument to substr() used
+as an lvalue, which is pretty strange.  Perhaps you forgot to
+dereference it first.  See L<perlfunc/substr>.
+
+=item Bareword "%s" refers to nonexistent package
+
+(W) You used a qualified bareword of the form C<Foo::>, but
+the compiler saw no other uses of that namespace before that point.
+Perhaps you need to predeclare a package?
+
+=item Can't redefine active sort subroutine %s
+
+(F) Perl optimizes the internal handling of sort subroutines and keeps
+pointers into them.  You tried to redefine one such sort subroutine when it
+was currently active, which is not allowed.  If you really want to do
+this, you should write C<sort { &func } @x> instead of C<sort func @x>.
+
+=item Can't use bareword ("%s") as %s ref while "strict refs" in use
+
+(F) Only hard references are allowed by "strict refs".  Symbolic references
+are disallowed.  See L<perlref>.
+
+=item Cannot resolve method `%s' overloading `%s' in package `%s'
+
+(P) Internal error trying to resolve overloading specified by a method
+name (as opposed to a subroutine reference).
+
+=item Constant subroutine %s redefined
+
+(S) You redefined a subroutine which had previously been eligible for
+inlining.  See L<perlsub/"Constant Functions"> for commentary and
+workarounds.
+
+=item Constant subroutine %s undefined
+
+(S) You undefined a subroutine which had previously been eligible for
+inlining.  See L<perlsub/"Constant Functions"> for commentary and
+workarounds.
+
+=item Copy method did not return a reference
+
+(F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
+
+=item Died
+
+(F) You passed die() an empty string (the equivalent of C<die "">) or
+you called it with no args and both C<$@> and C<$_> were empty.
+
+=item Exiting pseudo-block via %s
+
+(W) You are exiting a rather special block construct (like a sort block or
+subroutine) by unconventional means, such as a goto, or a loop control
+statement.  See L<perlfunc/sort>.
+
+=item Identifier too long
+
+(F) Perl limits identifiers (names for variables, functions, etc.) to
+252 characters for simple names, somewhat more for compound names (like
+C<$A::B>).  You've exceeded Perl's limits.  Future versions of Perl are
+likely to eliminate these arbitrary limitations.
+
+=item Illegal character %s (carriage return)
+
+(F) A carriage return character was found in the input.  This is an
+error, and not a warning, because carriage return characters can break
+multi-line strings, including here documents (e.g., C<print <<EOF;>).
+
+=item Illegal switch in PERL5OPT: %s
+
+(X) The PERL5OPT environment variable may only be used to set the
+following switches: B<-[DIMUdmw]>.
+
+=item Integer overflow in hex number
+
+(S) The literal hex number you have specified is too big for your
+architecture. On a 32-bit architecture the largest hex literal is
+0xFFFFFFFF.
+
+=item Integer overflow in octal number
+
+(S) The literal octal number you have specified is too big for your
+architecture. On a 32-bit architecture the largest octal literal is
+037777777777.
+
+=item internal error: glob failed
+
+(P) Something went wrong with the external program(s) used for C<glob>
+and C<< <*.c> >>.  This may mean that your csh (C shell) is
+broken.  If so, you should change all of the csh-related variables in
+config.sh:  If you have tcsh, make the variables refer to it as if it
+were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
+empty (except that C<d_csh> should be C<'undef'>) so that Perl will
+think csh is missing.  In either case, after editing config.sh, run
+C<./Configure -S> and rebuild Perl.
+
+=item Invalid conversion in %s: "%s"
+
+(W) Perl does not understand the given format conversion.
+See L<perlfunc/sprintf>.
+
+=item Invalid type in pack: '%s'
+
+(F) The given character is not a valid pack type.  See L<perlfunc/pack>.
+
+=item Invalid type in unpack: '%s'
+
+(F) The given character is not a valid unpack type.  See L<perlfunc/unpack>.
+
+=item Name "%s::%s" used only once: possible typo
+
+(W) Typographical errors often show up as unique variable names.
+If you had a good reason for having a unique name, then just mention
+it again somehow to suppress the message (the C<use vars> pragma is
+provided for just this purpose).
+
+=item Null picture in formline
+
+(F) The first argument to formline must be a valid format picture
+specification.  It was found to be empty, which probably means you
+supplied it an uninitialized value.  See L<perlform>.
+
+=item Offset outside string
+
+(F) You tried to do a read/write/send/recv operation with an offset
+pointing outside the buffer.  This is difficult to imagine.
+The sole exception to this is that C<sysread()>ing past the buffer
+will extend the buffer and zero pad the new area.
+
+=item Out of memory!
+
+(X|F) The malloc() function returned 0, indicating there was insufficient
+remaining memory (or virtual memory) to satisfy the request.
+
+The request was judged to be small, so the possibility to trap it
+depends on the way Perl was compiled.  By default it is not trappable.
+However, if compiled for this, Perl may use the contents of C<$^M> as
+an emergency pool after die()ing with this message.  In this case the
+error is trappable I<once>.
+
+=item Out of memory during request for %s
+
+(F) The malloc() function returned 0, indicating there was insufficient
+remaining memory (or virtual memory) to satisfy the request. However,
+the request was judged large enough (compile-time default is 64K), so
+a possibility to shut down by trapping this error is granted.
+
+=item panic: frexp
+
+(P) The library function frexp() failed, making printf("%f") impossible.
+
+=item Possible attempt to put comments in qw() list
+
+(W) qw() lists contain items separated by whitespace; as with literal
+strings, comment characters are not ignored, but are instead treated
+as literal data.  (You may have used different delimiters than the
+parentheses shown here; braces are also frequently used.)
+
+You probably wrote something like this:
+
+    @list = qw(
+        a # a comment
+        b # another comment
+    );
+
+when you should have written this:
+
+    @list = qw(
+        a
+        b
+    );
+
+If you really want comments, build your list the
+old-fashioned way, with quotes and commas:
+
+    @list = (
+        'a',    # a comment
+        'b',    # another comment
+    );
+
+=item Possible attempt to separate words with commas
+
+(W) qw() lists contain items separated by whitespace; therefore commas
+aren't needed to separate the items. (You may have used different
+delimiters than the parentheses shown here; braces are also frequently
+used.)
+
+You probably wrote something like this:
+
+    qw! a, b, c !;
+
+which puts literal commas into some of the list items.  Write it without
+commas if you don't want them to appear in your data:
+
+    qw! a b c !;
+
+=item Scalar value @%s{%s} better written as $%s{%s}
+
+(W) You've used a hash slice (indicated by @) to select a single element of
+a hash.  Generally it's better to ask for a scalar value (indicated by $).
+The difference is that C<$foo{&bar}> always behaves like a scalar, both when
+assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
+like a list when you assign to it, and provides a list context to its
+subscript, which can do weird things if you're expecting only one subscript.
+
+=item Stub found while resolving method `%s' overloading `%s' in %s
+
+(P) Overloading resolution over @ISA tree may be broken by importing stubs.
+Stubs should never be implicitly created, but explicit calls to C<can>
+may break this.
+
+=item Too late for "B<-T>" option
+
+(X) The #! line (or local equivalent) in a Perl script contains the
+B<-T> option, but Perl was not invoked with B<-T> in its argument
+list.  This is an error because, by the time Perl discovers a B<-T> in
+a script, it's too late to properly taint everything from the
+environment.  So Perl gives up.
+
+=item untie attempted while %d inner references still exist
+
+(W) A copy of the object returned from C<tie> (or C<tied>) was still
+valid when C<untie> was called.
+
+=item Unrecognized character %s
+
+(F) The Perl parser has no idea what to do with the specified character
+in your Perl script (or eval).  Perhaps you tried to run a compressed
+script, a binary program, or a directory as a Perl program.
+
+=item Unsupported function fork
+
+(F) Your version of executable does not support forking.
+
+Note that under some systems, like OS/2, there may be different flavors of
+Perl executables, some of which may support fork, some not. Try changing
+the name you call Perl by to C<perl_>, C<perl__>, and so on.
+
+=item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
+
+(D) Perl versions before 5.004 misinterpreted any type marker followed
+by "$" and a digit.  For example, "$$0" was incorrectly taken to mean
+"${$}0" instead of "${$0}".  This bug is (mostly) fixed in Perl 5.004.
+
+However, the developers of Perl 5.004 could not fix this bug completely,
+because at least two widely-used modules depend on the old meaning of
+"$$0" in a string.  So Perl 5.004 still interprets "$$<digit>" in the
+old (broken) way inside strings; but it generates this message as a
+warning.  And in Perl 5.005, this special treatment will cease.
+
+=item Value of %s can be "0"; test with defined()
+
+(W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
+or C<readdir()> as a boolean value.  Each of these constructs can return a
+value of "0"; that would make the conditional expression false, which is
+probably not what you intended.  When using these constructs in conditional
+expressions, test their values with the C<defined> operator.
+
+=item Variable "%s" may be unavailable
+
+(W) An inner (nested) I<anonymous> subroutine is inside a I<named>
+subroutine, and outside that is another subroutine; and the anonymous
+(innermost) subroutine is referencing a lexical variable defined in
+the outermost subroutine.  For example:
+
+   sub outermost { my $a; sub middle { sub { $a } } }
+
+If the anonymous subroutine is called or referenced (directly or
+indirectly) from the outermost subroutine, it will share the variable
+as you would expect.  But if the anonymous subroutine is called or
+referenced when the outermost subroutine is not active, it will see
+the value of the shared variable as it was before and during the
+*first* call to the outermost subroutine, which is probably not what
+you want.
+
+In these circumstances, it is usually best to make the middle
+subroutine anonymous, using the C<sub {}> syntax.  Perl has specific
+support for shared variables in nested anonymous subroutines; a named
+subroutine in between interferes with this feature.
+
+=item Variable "%s" will not stay shared
+
+(W) An inner (nested) I<named> subroutine is referencing a lexical
+variable defined in an outer subroutine.
+
+When the inner subroutine is called, it will probably see the value of
+the outer subroutine's variable as it was before and during the
+*first* call to the outer subroutine; in this case, after the first
+call to the outer subroutine is complete, the inner and outer
+subroutines will no longer share a common value for the variable.  In
+other words, the variable will no longer be shared.
+
+Furthermore, if the outer subroutine is anonymous and references a
+lexical variable outside itself, then the outer and inner subroutines
+will I<never> share the given variable.
+
+This problem can usually be solved by making the inner subroutine
+anonymous, using the C<sub {}> syntax.  When inner anonymous subs that
+reference variables in outer subroutines are called or referenced,
+they are automatically rebound to the current values of such
+variables.
+
+=item Warning: something's wrong
+
+(W) You passed warn() an empty string (the equivalent of C<warn "">) or
+you called it with no args and C<$_> was empty.
+
+=item Ill-formed logical name |%s| in prime_env_iter
+
+(W) A warning peculiar to VMS.  A logical name was encountered when preparing
+to iterate over %ENV which violates the syntactic rules governing logical
+names.  Since it cannot be translated normally, it is skipped, and will not
+appear in %ENV.  This may be a benign occurrence, as some software packages
+might directly modify logical name tables and introduce nonstandard names,
+or it may indicate that a logical name table has been corrupted.
+
+=item Got an error from DosAllocMem
+
+(P) An error peculiar to OS/2.  Most probably you're using an obsolete
+version of Perl, and this should not happen anyway.
+
+=item Malformed PERLLIB_PREFIX
+
+(F) An error peculiar to OS/2.  PERLLIB_PREFIX should be of the form
+
+    prefix1;prefix2
+
+or
+
+    prefix1 prefix2
+
+with nonempty prefix1 and prefix2.  If C<prefix1> is indeed a prefix
+of a builtin library search path, prefix2 is substituted.  The error
+may appear if components are not found, or are too long.  See
+"PERLLIB_PREFIX" in F<README.os2>.
+
+=item PERL_SH_DIR too long
+
+(F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
+C<sh>-shell in.  See "PERL_SH_DIR" in F<README.os2>.
+
+=item Process terminated by SIG%s
+
+(W) This is a standard message issued by OS/2 applications, while *nix
+applications die in silence.  It is considered a feature of the OS/2
+port.  One can easily disable this by appropriate sighandlers, see
+L<perlipc/"Signals">.  See also "Process terminated by SIGTERM/SIGINT"
+in F<README.os2>.
+
+=back
+
+=head1 BUGS
+
+If you find what you think is a bug, you might check the headers of
+recently posted articles in the comp.lang.perl.misc newsgroup.
+There may also be information at http://www.perl.com/perl/ , the Perl
+Home Page.
+
+If you believe you have an unreported bug, please run the B<perlbug>
+program included with your release.  Make sure you 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 <F<perlbug@perl.com>> to be
+analysed by the Perl porting team.
+
+=head1 SEE ALSO
+
+The F<Changes> file for exhaustive details on what changed.
+
+The F<INSTALL> file for how to build Perl.  This file has been
+significantly updated for 5.004, so even veteran users should
+look through it.
+
+The F<README> file for general stuff.
+
+The F<Copying> file for copyright information.
+
+=head1 HISTORY
+
+Constructed by Tom Christiansen, grabbing material with permission
+from innumerable contributors, with kibitzing by more than a few Perl
+porters.
+
+Last update: Wed May 14 11:14:09 EDT 1997