Creating custom browse facets with the Display Plugin

<p>I am building a custom plugin that needs to add new facets to the browse page. The ahgDisplayPlugin handles facet rendering, but I want to add a facet for our custom metadata field (conservation priority).</p><p>I've looked at the facet configuration in <code>display_facet_config</code> table, but I'm not sure how to register a new facet type that queries a custom table.</p><p>Has anyone extended the facet system?</p>