backward-word

The target location for the insertion cursor is the first non-token separator character after the first token separator character to the left of the present position or the beginning of the line. Token separator characters are given by the tokenSeps resource. If the insertion cursor is already at the beginning of a word, the target location is the beginning of the previous word.

Typically, the insertion cursor just moves to the target location. However, the command is parser-initiating and parsing may eliminate the target location; in this case, the insertion cursor moves to a nearby location.