http://irsa.ipac.caltech.edu/applications/DDGEN/Doc/ipac_tbl.html
says: Comment lines should have no more than 80 characters.
(2 characters are needed for `\ ` to mark a line as a comment.)
I guess since it says "should" and not "must" I could downgrade this to a warning.
However, the idea here is (like in votable) to be loose on input but write tables strictly adhering to the documented specification.
Users can always decide to break their comment lines, but I don't want to decide automatically where to break them.

Would you prefer a warning?