[geokon]

"Surely this is true of all markup languages. How you would represent this visually in a document?"

Not to be snarky, but the ML in XML and HTML stands for markup language..

I'd like my markup to be easy to read and also to map to a tree hierarchy. This seems essential for parsing and anything related to literate programming and reusing "blocks"

Like when I drop in a org mode clock (for logging time in my work logbook), without a tree hierarchy I have no means of binding the time to my description of the work I did. I mean... I see in visually, but its not programmatically linked as an attribute of that text block.

You can kinda get around with pepperin headers everywhere, but it's not as flexible