Syntax:  bf(%debug) 

Provide tt(parse) and its support functions with debugging code,
showing the actual parsing process on the standard output
stream. 

When specified, debug output is shown by default, but its activity may be
controlled using the tt(setDebug(bool on-off)) or tt(setDebug(DebugMode_))
members. Note that no tt(#ifdef DEBUG) macros are used anymore. Rerun b()
without the bf(--debug) option to generate an equivalent parser not containing
the debugging code.
