Delegation.

I found it interesting that this let me easily move around which helper class or which of a set of collaborating classes actually implemented the thing.

B and C contain references to the A parent, and the 'has' 'handles' construct can specify to delegate all the functions that A is providing.

Likewise, the variable in A that holds its B also delegates functions that B implements.

Methods in either class can just refer to functions in the overall complex, and not care which object is handling it. If you move a function, you change the 'has' lines but no other code!

This is inside what you are calling B:

has tag_formatter => (
    is => 'ro',
    handles => [ qw( format_tag escape filter link_prefixes)],
    required => 1,
    weak_ref => 1,  # normally points back to parent Creole object
    );

 has config_keeper => (
    is => 'ro',
    handles => [ qw( placeholder_callback link_mapper image_mapper)],
    required => 1,
    weak_ref => 1,  # normally points back to parent Creole object
    );
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Both of those are pointing back to A. But I could further break up A and make the tag formatter into yet another separate class later!

—John