Having recently noticed that using <del> aka <delete> aka <rubout>
could work as a command, assign it to #terrain. #terrain was the
only command in the "game" subset of commands as shown by '? i'
that didn't have any key assignment.
Since <delete> might be swapped with <backspace> on some terminals
and is a keypad key on the typical PC keyboard, it might not work
reliably depending on nethack's number_pad mode or the hardware
Num-Lock setting. Players in either of those situations haven't
lost anything; they can still use extended command #terrain.
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