font-lock-beginning-of-syntax-function semi-obsolete?

[Lute Kamstra]

I'm updating lispref/modex.texi and noticed that the docstring of
font-lock-beginning-of-syntax-function says that it is semi-obsolete:

  *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, the beginning of the buffer is used, which is
  always correct but tends to be slow.
  This is normally set via `font-lock-defaults'.
  This variable is semi-obsolete; we recommend setting
  `syntax-begin-function' instead.

So, how do you make Font Lock use the function in the variable
syntax-begin-function to move to top level?

Lute.