Non-nil means use this function to move back outside all constructs.
When called with no args it should move point backward to a place which
is not in a string or comment and not within any bracket-pairs (or else,
a place such that any bracket-pairs outside it can be ignored for Emacs
syntax analysis and fontification).
If this is nil, Font Lock uses `syntax-begin-function' to move back
outside of any comment, string, or sexp. This variable is semi-obsolete;
we recommend setting `syntax-begin-function' instead.
This is normally set via `font-lock-defaults'.