generate ids for all elements to allow more specific "post-hoc" external linking

[joernhees]

currently only sections get ids... would it be possible to automagically create a UUID3/5 (based on the paragraph's content) for each paragraph? that way post-hoc linking can become much more precise... (so i can precisely link stuff the author at the time didn't explicitly prepare to be quoted/linked)

also see discussion on linkedresearch gitter

[joernhees]

(note that UUID4 in this case wouldn't be well suited as all ids would change every time the document is re-generated)