current buffer. It calls @var{function} before calling the default
fontification functions, and gives it two arguments, @var{start} and
@var{end}, which specify the region to be fontified or refontified.
+If @var{function} performs fontifications, it can return a list of the
+form @w{@code{(jit-lock-bounds @var{beg} . @var{end})}}, to indicate
+the bounds of the region it actually fontified; JIT font-lock will use
+this information to optimize subsequent redisplay cycles and regions
+of buffer text it will pass to future calls to @var{function}.
The optional argument @var{contextual}, if non-@code{nil}, forces Font
Lock mode to always refontify a syntactically relevant part of the
(defvar jit-lock-functions nil
"Special hook run to do the actual fontification.
The functions are called with two arguments:
-the START and END of the region to fontify.")
+the START and END of the region to fontify.
+Each function can return a list of the form (jit-lock-bounds BEG . END),
+to indicate the bounds of the region it actually fontified;
+JIT font-lock will use this information to optimize redisplay cycles.")
(defvar-local jit-lock-context-unfontify-pos nil
"Consider text after this position as contextually unfontified.
"Register FUN as a fontification function to be called in this buffer.
FUN will be called with two arguments START and END indicating the region
that needs to be (re)fontified.
-If non-nil, CONTEXTUAL means that a contextual fontification would be useful."
+If non-nil, CONTEXTUAL means that a contextual fontification would be useful.
+FUN can return a list of the form (jit-lock-bounds BEG . END),
+to indicate the bounds of the region it actually fontified; JIT
+font-lock will use this information to optimize redisplay cycles."
(add-hook 'jit-lock-functions fun nil t)
(when (and contextual jit-lock-contextually)
(setq-local jit-lock-contextually t))