различия между GNU roff и AT&T troff (differences between GNU roff and AT&T troff)
Отладка (Debugging)
In addition to AT&T troff debugging features, groff emits more
error diagnostics when syntactical or semantic nonsense is
encountered and supports several categories of warning; the
output of these can be selectively suppressed with .warn (and see
the -E, -w, and -W options of troff(1)). Backtraces can be
automatically produced when errors or warnings occur (the -b
option of troff(1)) or generated on demand (.backtrace).
groff also adds more flexible diagnostic output requests (.tmc
and .tm1). More aspects of formatter state can be examined with
requests that write lists of defined registers (.pnr),
environments (.pev), and page location traps (.ptr) to the
standard error stream.
