Is there documentation for PlugIn Handlers?

Is there any documentation on PlugIn.Handlers ? In particular:

  • What is the proper way to register via the plugin manifest
  • What is the lifecycle ? The canvas.onGraphicChanged(handler) appears to be the only way to use them.
  • What is the purpose of the handler.willAttach() callback - the value it returns is then passed with each property change notification, but it’s not clear what this can be used for.
  • What is the purpose of the “Handlers” section in the Automation menu ? It shows an item for each registered handler, but that doesn’t do anything.
  • How to avoid Omnigraffle crashing with an attached handler when deleting graphics from the canvas.

I have managed to register an automation handler in my plugin manifest and attach it to a canvas.
It receives the callback whenever properties of graphics on the canvas change - this is exactly what I am looking for !

Per Greg Titus over on the Slack [1]:

automation handlers aren’t fully implemented in OmniGraffle. Exposing the menu item and API reference section are an oversight on our part

So this question can wait :) !