skip-syntax-backward

skip-syntax-backward is a built-in function in `C source code'.

(skip-syntax-backward SYNTAX &optional LIM)

Move point backward across chars in specified syntax classes.
SYNTAX is a string of syntax code characters.
Stop on reaching a char whose syntax is not in SYNTAX, or at position LIM.
If SYNTAX starts with ^, skip characters whose syntax is NOT in SYNTAX.
This function returns either zero or a negative number, and the absolute value
of this is the distance traveled.