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}

sub bits {
    my $on = shift;
    my $bits = 0;
    my $turning_all_off = ! @_ && ! $on;
    my $seen_Debug = 0;
    my $seen_debug = 0;
    if ($turning_all_off) {

        # Pretend were called with certain parameters, which are best dealt
        # with that way.
        push @_, keys %bitmask; # taint and eval
        push @_, 'strict';
    }

    # Process each subpragma parameter
   ARG:
    foreach my $idx (0..$#_){
        my $s=$_[$idx];
        if ($s eq 'Debug' or $s eq 'Debugcolor') {
            if (! $seen_Debug) {
                $seen_Debug = 1;

                # Reset to nothing, and then add what follows.  $seen_Debug
                # allows, though unlikely someone would do it, more than one
                # Debug and flags in the arguments
                ${^RE_DEBUG_FLAGS} = 0;
            }
            setcolor() if $s =~/color/i;
            for my $idx ($idx+1..$#_) {
                if ($flags{$_[$idx]}) {
                    if ($on) {
                        ${^RE_DEBUG_FLAGS} |= $flags{$_[$idx]};
                    } else {
                        ${^RE_DEBUG_FLAGS} &= ~ $flags{$_[$idx]};
                    }
                } else {
                    require Carp;
                    Carp::carp("Unknown \"re\" Debug flag '$_[$idx]', possible flags: ",
                               join(", ",sort keys %flags ) );
                }
            }
            _load_unload($on ? 1 : ${^RE_DEBUG_FLAGS});
            last;
        } elsif ($s eq 'debug' or $s eq 'debugcolor') {

            # These default flags should be kept in sync with the same values
            # in regcomp.h
            ${^RE_DEBUG_FLAGS} = $flags{'EXECUTE'} | $flags{'DUMP'};
	    setcolor() if $s =~/color/i;
	    _load_unload($on);
            $seen_debug = 1;
        } elsif (exists $bitmask{$s}) {
	    $bits |= $bitmask{$s};
	} elsif ($EXPORT_OK{$s}) {
	    require Exporter;
	    re->export_to_level(2, 're', $s);
        } elsif ($s eq 'strict') {
            if ($on) {
                $^H{reflags} |= $reflags{$s};
                warnings::warnif('experimental::re_strict',
                                 "\"use re 'strict'\" is experimental");

                # Turn on warnings if not already done.
                if (! warnings::enabled('regexp')) {
                    require warnings;
                    warnings->import('regexp');
                    $^H{re_strict} = 1;
                }
            }
            else {
                $^H{reflags} &= ~$reflags{$s} if $^H{reflags};

                # Turn off warnings if we turned them on.
                warnings->unimport('regexp') if $^H{re_strict};
            }
	    if ($^H{reflags}) {
                $^H |= $flags_hint;
            }
            else {
                $^H &= ~$flags_hint;
            }
	} elsif ($s =~ s/^\///) {
	    my $reflags = $^H{reflags} || 0;
	    my $seen_charset;
            my $x_count = 0;
	    while ($s =~ m/( . )/gx) {
                local $_ = $1;
		if (/[adul]/) {
                    # The 'a' may be repeated; hide this from the rest of the
                    # code by counting and getting rid of all of them, then
                    # changing to 'aa' if there is a repeat.
                    if ($_ eq 'a') {
                        my $sav_pos = pos $s;
                        my $a_count = $s =~ s/a//g;
                        pos $s = $sav_pos - 1;  # -1 because got rid of the 'a'
                        if ($a_count > 2) {
			    require Carp;
                            Carp::carp(
                            qq 'The "a" flag may only appear a maximum of twice'
                            );
                        }
                        elsif ($a_count == 2) {
                            $_ = 'aa';
                        }
                    }
		    if ($on) {
			if ($seen_charset) {
			    require Carp;
                            if ($seen_charset ne $_) {
                                Carp::carp(
                                qq 'The "$seen_charset" and "$_" flags '
                                .qq 'are exclusive'
                                );
                            }
                            else {
                                Carp::carp(
                                qq 'The "$seen_charset" flag may not appear '
                                .qq 'twice'
                                );
                            }
			}
			$^H{reflags_charset} = $reflags{$_};
			$seen_charset = $_;
		    }
		    else {
			delete $^H{reflags_charset}
                                     if defined $^H{reflags_charset}
                                        && $^H{reflags_charset} == $reflags{$_};
		    }
		} elsif (exists $reflags{$_}) {
                    if ($_ eq 'x') {
                        $x_count++;
                        if ($x_count > 2) {
			    require Carp;
                            Carp::carp(
                            qq 'The "x" flag may only appear a maximum of twice'
                            );
                        }
                        elsif ($x_count == 2) {
                            $_ = 'xx';  # First time through got the /x
                        }
                    }

                    $on
		      ? $reflags |= $reflags{$_}
		      : ($reflags &= ~$reflags{$_});
		} else {
		    require Carp;
		    Carp::carp(
		     qq'Unknown regular expression flag "$_"'
		    );
		    next ARG;
		}
	    }
	    ($^H{reflags} = $reflags or defined $^H{reflags_charset})
	                    ? $^H |= $flags_hint
	                    : ($^H &= ~$flags_hint);
	} else {
	    require Carp;
            if ($seen_debug && defined $flags{$s}) {
                Carp::carp("Use \"Debug\" not \"debug\", to list debug types"
                         . " in \"re\".  \"$s\" ignored");
            }
            else {
                Carp::carp("Unknown \"re\" subpragma '$s' (known ones are: ",
                       join(', ', map {qq('$_')} 'debug', 'debugcolor', sort keys %bitmask),
                       ")");
            }
	}
    }

    if ($turning_all_off) {
        _load_unload(0);
        $^H{reflags} = 0;
        $^H{reflags_charset} = 0;
        $^H &= ~$flags_hint;
    }

    $bits;
}

sub import {
    shift;
    $^H |= bits(1, @_);
}

sub unimport {
    shift;
    $^H &= ~ bits(0, @_);
}

1;

__END__

=head1 NAME

re - Perl pragma to alter regular expression behaviour

=head1 SYNOPSIS

    use re 'taint';
    ($x) = ($^X =~ /^(.*)$/s);     # $x is tainted here

    $pat = '(?{ $foo = 1 })';
    use re 'eval';
    /foo${pat}bar/;		   # won't fail (when not under -T
                                   # switch)

    {
	no re 'taint';		   # the default
	($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here

	no re 'eval';		   # the default
	/foo${pat}bar/;		   # disallowed (with or without -T