$bgn_target = "<!--begin node-->";
$bgn_offset = index( $_, $bgn_target ) + length( $bgn_target );
$keep_length = rindex( $_, "<!--end node-->" ) - $bgn_offset;
$keep_string = substr( $_, $bgn_offset, $keep_length );

##</code><code>##

  /<!--begin node-->(.*)<!--end node-->/