> This left me wondering if it's a Groff extension, but I couldn't find any > mention of it in *groff_diff*. Or is there something else I'm missing?
Have a look at the `Miscellaneous' section in the `groff_diff' man page! The `!' is a NOT operator (which isn't new), and the GNU troff extension `d' is documented there. The canonical documentation, BTW, are the groff info files, cf. http://www.gnu.org/software/groff/manual/ Werner
