See POSIX/GNU, 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:
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.