Have a quick question, the answer for which seems to be obvious, but just wanting to check and maybe hope I'm wrong.

#!/usr/bin/perl
use strict; use warnings;
use P; 

my $intxt;
$intxt = << 'TXT' ;
<package type="rpm">
  <name>7kaa-music</name>
  <url>http://7kfans.com/</url>
TXT
;

sub REindex($$;$) {   #like 'index', except substr is RE
  my ($str,$ss)=(shift, shift);
  my $p = @_ ? shift:0;
  $str =~ m{^.{$p,$p}($ss+)} ? length $1 : -1;
}

my @lines=split "\n", $intxt;

my $ln;
my $lineno=0;

sub getln() {
  return $lineno<@lines ? $lines[$lineno++] : undef;
}

my $ttag;

  sub getnxt_tagln(); local * getnxt_tagln;
  *getnxt_tagln = sub () {
    do {
      $_=getln();
      defined $_ or return undef;
    } until m{^\s*<(/?\w+)};
    $ttag=$1;
  };

  my $tag;
 NXTPKG:
  while (getnxt_tagln()) {      # why '$1' null?
    $ln = $_; $tag = $1;
    Pe "_=%s, ttag=%s, tag=%s", $_, $ttag, $tag;
  }
# vim: ts=2 sw=2 ai number
[download]

My question concerns the comment after the NXTPKG line: why '$1' null (∄)?

When I run this:

_=<package type="rpm">, ttag=package, tag=∄;
_=  <name>7kaa-music</name>, ttag=name, tag=∄;
_=  <url>http://7kfans.com/</url>, ttag=url, tag=∄;

tag is null/undef when I get out of my inline-sub. I can get around it by assigning $1 to $ttag, but I don't have any other Regex's that should be clearing '$1'. Seems a bit weird to have the end of a local sub clear '$1', yet that seems to be what is happening. Why? What was the logic of forcing/doing that?

tnx!