example, when a buffer change has changed the syntactic meaning of text
on an earlier line.
-You can enlarge (or even reduce) the region to fontify by setting either
-of the following variables:
+You can enlarge (or even reduce) the region to fontify by setting @c either of
+the following variables:
@defvar font-lock-extend-region-function
This buffer-local variable is either @code{nil} or is a function that
@var{end}, and @var{old-len} from after-change-functions (@pxref{Change
Hooks}). It should return either a cons of the beginning and end buffer
positions (in that order) of the region to fontify, or @code{nil} (which
-directs the caller to fontify the default region). This function need
-not preserve point or the match-data, but must preserve the current
-restriction. The region it returns may start or end in the middle of a
-line.
+directs the caller to fontify the default region). This function needs
+to preserve point, the match-data, and the current restriction.
+The region it returns may start or end in the middle of a line.
Since this function is called after every buffer change, it should be
reasonably fast.