Quotes take precedence over all other things. What is a "troff symbol"? I can only think of troff escapes, which can only appear in quotes , so are not eqn things in their own right. (In user errors they may be seen as punctuation, etc.) Ditto for "eqn symbol"? Perhaps the union of some or all of the things that follow in the list? Ditto again for "mathematical punctuation". Comma is one example I can think of. Apostrophe, read as "prime", may be another. Are there more? Is "surrounded by" inclusive or exclusive? Why is "character" distinguished from "word"? The ??? question bears on the issue of whether sintheta is one thing or two. The word "maximal" will probably figure in the answer Another (sticky) point is how punctuation sticks to an adjacent thing. For example, eqn inserts space in (a,b), but keeps the whole thing(?) together in 2 sup (a,b). Doug