Another idea: use CSV comment to embed any neccessary metadata. According to http://stackoverflow.com/questions/1961006/can-a-csv-file-have-a-comment , CSV comment is not standardized, however.

Why it might be useful: I am thinking about writing some sort of CSV reader and writer such that it can go back and forth between CSV and pandoc AST "losslessly".

And since CSV comment is not standize, feel free to comment on what syntax might be best.