Speaking of keys, I vaguely remember there being a key which, when held down and a direction key pressed along with it, would make the digger dig on the square

Speaking of keys, I vaguely remember there being a key which, when held down and a direction key pressed along with it, would make the digger dig on the square adjacent in that direction. If the target tile was soil or diamonds, it would disappear, while the action would not have any effect on the other types of tiles. I tried the usual SPC/CTRL/ALT, but they don't seem to work in this way. Am I misremembering this feature, or is it simply not part of this implementation?