And below is how to do it with the optional subrule. It even provides better error messages. 

#!/usr/bin/env perl

use strict;
use warnings;
use feature qw( say );

use Parse::RecDescent qw( );

my $grammar = <<'__EOI__';

  myrule    : <rulevar: local $failed = 1>
  myrule    : 'stuff' mysubrule(?) <reject:$failed>
  mysubrule : 'ID' <commit> '[' ']'
            | <error?> { $failed = 0; } <reject>

__EOI__

my $parser = Parse::RecDescent->new($grammar)
   or die;

for my $text ("stuff ID something", "stuff something") {
   say "====================";
   say "$text";
   say "--------------------";
   say $parser->myrule($text) ? 'pass' : 'fail';
}

[download]
====================
stuff ID something
--------------------

       ERROR (line 1): Invalid mysubrule: Was expecting '[' but found
                       "something" instead
fail
====================
stuff something
--------------------
pass

[download]

In reply to Re^2: Parse::Recdescent optional subrule commit by ikegami
in thread Parse::Recdescent optional subrule commit by campugnatus

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