✏ EDIT: version.pm

#!perl -w
package version;

use 5.006002;
use strict;
use warnings::register;
if ($] >= 5.015) {
    warnings::register_categories(qw/version/);
}

our $VERSION = '0.9933';
our $CLASS = 'version';
our (@ISA, $STRICT, $LAX);

# !!!!Delete this next block completely when adding to Perl core!!!!
{
    local $SIG{'__DIE__'};
    eval "use version::vxs $VERSION";
    if ( $@ ) { # don't have the XS version installed
	eval "use version::vpp $VERSION"; # don't tempt fate
	die "$@" if ( $@ );
	push @ISA, "version::vpp";
	local $^W;
	*version::qv = \&version::vpp::qv;
	*version::declare = \&version::vpp::declare;
	*version::_VERSION = \&version::vpp::_VERSION;
	*version::vcmp = \&version::vpp::vcmp;
	*version::new = \&version::vpp::new;
	*version::numify = \&version::vpp::numify;
	*version::normal = \&version::vpp::normal;
	*version::to_decimal = \&version::vpp::to_decimal;
	*version::to_dotted_decimal = \&version::vpp::to_dotted_decimal;
	*version::tuple = \&version::vpp::tuple;
	*version::from_tuple = \&version::vpp::from_tuple;
	if ($] >= 5.009000) {
	    no strict 'refs';
	    *version::stringify = \&version::vpp::stringify;
	    *{'version::(""'} = \&version::vpp::stringify;
	    *{'version::(<=>'} = \&version::vpp::vcmp;
	    *{'version::(cmp'} = \&version::vpp::vcmp;
	    *version::parse = \&version::vpp::parse;
	}
    }
    else { # use XS module
	push @ISA, "version::vxs";
	local $^W;
	*version::declare = \&version::vxs::declare;
	*version::qv = \&version::vxs::qv;
	*version::_VERSION = \&version::vxs::_VERSION;
	*version::vcmp = \&version::vxs::VCMP;
	*version::new = \&version::vxs::new;
	*version::numify = \&version::vxs::numify;
	*version::normal = \&version::vxs::normal;
	*version::to_decimal = \&version::vxs::to_decimal;
	*version::to_dotted_decimal = \&version::vxs::to_dotted_decimal;
	*version::tuple = \&version::vxs::tuple;
	*version::from_tuple = \&version::vxs::from_tuple;
	if ($] >= 5.009000) {
	    no strict 'refs';
	    *version::stringify = \&version::vxs::stringify;
	    *{'version::(""'} = \&version::vxs::stringify;
	    *{'version::(<=>'} = \&version::vxs::VCMP;
	    *{'version::(cmp'} = \&version::vxs::VCMP;
	    *version::parse = \&version::vxs::parse;
	}
    }
}

# avoid using Exporter
require version::regex;
*version::is_lax = \&version::regex::is_lax;
*version::is_strict = \&version::regex::is_strict;
*LAX = \$version::regex::LAX;
*LAX_DECIMAL_VERSION = \$version::regex::LAX_DECIMAL_VERSION;
*LAX_DOTTED_DECIMAL_VERSION = \$version::regex::LAX_DOTTED_DECIMAL_VERSION;
*STRICT = \$version::regex::STRICT;
*STRICT_DECIMAL_VERSION = \$version::regex::STRICT_DECIMAL_VERSION;
*STRICT_DOTTED_DECIMAL_VERSION = \$version::regex::STRICT_DOTTED_DECIMAL_VERSION;

sub import {
    no strict 'refs';
    my ($class) = shift;

# Set up any derived class
    unless ($class eq $CLASS) {
	local $^W;
	*{$class.'::declare'} =  \&{$CLASS.'::declare'};
	*{$class.'::qv'} = \&{$CLASS.'::qv'};
    }

my %args;
    if (@_) { # any remaining terms are arguments
	map { $args{$_} = 1 } @_
    }
    else { # no parameters at all on use line
	%args =
	(
	    qv => 1,
	    'UNIVERSAL::VERSION' => 1,
	);
    }

my $callpkg = caller();

if (exists($args{declare})) {
	*{$callpkg.'::declare'} =
	    sub {return $class->declare(shift) }
	  unless defined(&{$callpkg.'::declare'});
    }

if (exists($args{qv})) {
	*{$callpkg.'::qv'} =
	    sub {return $class->qv(shift) }
	  unless defined(&{$callpkg.'::qv'});
    }

if (exists($args{'UNIVERSAL::VERSION'})) {
	local $^W;
	*UNIVERSAL::VERSION
		= \&{$CLASS.'::_VERSION'};
    }

if (exists($args{'VERSION'})) {
	*{$callpkg.'::VERSION'} = \&{$CLASS.'::_VERSION'};
    }

if (exists($args{'is_strict'})) {
	*{$callpkg.'::is_strict'} = \&{$CLASS.'::is_strict'}
	  unless defined(&{$callpkg.'::is_strict'});
    }

if (exists($args{'is_lax'})) {
	*{$callpkg.'::is_lax'} = \&{$CLASS.'::is_lax'}
	  unless defined(&{$callpkg.'::is_lax'});
    }
}

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