"Usage" was one of those lovely ideas, one exposure to which flips its status from unknown to eternal truth. I am sure my first exposure was on Unix, but I don't remember when. Perhaps because it radically departs from Ken's "?" in qed/ed, I have subconsciously attributed it to Dennis. The genius of "usage" and "?" is that they don't attempt to tell one what's wrong. Most diagnostics cite a rule or hidden limit that's been violated or describe the mistake (e.g. "missing semicolon") , sometimes raising more questions than they answer. Another non-descriptive style of error message that I admired was that of Berkeley Pascal's syntax diagnostics. When the LR parser could not proceed, it reported where, and automatically provided a sample token that would allow the parsing to progress. I found this uniform convention to be at least as informative as distinct hand-crafted messages, which almost by definition can't foresee every contingency. Alas, this elegant scheme seems not to have inspired imitators. Doug