How to catch a non-file (eg. ui.print) buffer upon its creation (or close to that moment)?

[metaleap]

I noticed that buffers of opened-actual-files have a non-nil buffer.filename and ui.print-etc buffers never have one.

But I also noticed that on any buffer's BUFFER_NEW or its first BUFFER_AFTER_SWITCH, they all have no buffer.filename yet. Even the actual-file kind of buffers that I presume get it populated just afterwards.

Is there any event I'm missing that is only-once per buffer and early in its lifecycle, but where its file-ness is already populated?

[metaleap]

Already got it, just gotta connect to events.BUFFER_AFTER_SWITCH from inside the INITIALIZED handler 😁