I'm not sure I understand the question. Maybe this code example is what you're looking for?

use strict;
use List::Extract 'extract';

sub MODIFY_CODE_ATTRIBUTES {
  my $class = shift;
  my ($cref, @attrs) = @_;

  my ($bent) = extract { /^Bent\b/ } @attrs;

  if (defined $bent) {
    print "Recognized attribute: $bent\n";
  }

  return @attrs; # Unrecognized.
}

sub foo :Bent;
sub bar :Bent(named) { 1 }

my $code = sub :Bent(anonymous) { 1 }

__END__
Recognized attribute: Bent
Recognized attribute: Bent(named)
Recognized attribute: Bent(anonymous)
[download]

This is documented in attributes under "Package-specific Attribute Handling".

What to do once a subroutine attribute is recognized is a completely different story. :-)

lodin