Where to put things like todos, metadata, internal remarks?

Is there a place ( ideally per slide ) where i could put my todos/ annotations/ working instructions as metadata for the internal workflow process?

For example where could an author put his messages to a graphic-designer about animations he wishes to have at a certain place, something like that.

I think, slide - annotations is not a good choice for this because they have another target group (end-user) and they are mixed up with audio-text ( subtitles ) when exported.

thanks in advance!

Ingo