How to connect a customElement to a Message Filter custom action?

Hi,

in recent versions of Thunderbird the XBL bindings have been removed; my extension used these to add a custom message filter action, so that part of it is no longer working.

The documentation says the bindings need to be replaces by a custom element, which is fine, but I can’t really find any information on how to link that custom element to the custom filter action.

The patch diffs for the removal of the relevant part https://bugzilla.mozilla.org/show_bug.cgi?id=1489172 show me how to create a customElement for this, but not how to get it picked up by my custom Filter Action…

Does anyone know if there is an example of this, and/or an extension that uses custom message filters with arguments in TB 68+, where I can take a peek?