introduce concept of dev-mode ?
I propose an option to have different "mode" of drawing the notes, which is a bit like the card mode of gorilla-notes:

Specially useful for me is the line number, as this allows me to find notes in Emacs quickly, as I as I have line numbers switched on in Emacs.
As id add some "technical" information, we could maybe call it "devmode" or similar.
This opens of course the general question, how and if we want allow end users to customize the output.
Currently we have already the render-src? config.
Should we have an other config dev-mode which enables the addition of the horizontal line and the line number, duration ?
Great idea.
I think it makes sense to be able to define such things through the config, as you suggested.