See Extensions in gawk Not in POSIX awk,
for a summary of the GNU extensions to the awk language and program.
All of these features can be turned off by invoking gawk with the
--traditional option or with the --posix option.
If gawk is compiled for debugging with ‘-DDEBUG’, then there
is one more option available on the command line:
-Y--parsedebugPrint out the parse stack information as the program is being parsed.
This option is intended only for serious gawk developers
and not for the casual user. It probably has not even been compiled into
your version of gawk, since it slows down execution.