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38.12.7 Automatic Face Assignment

This hook is used for automatically assigning faces to text in the buffer. It is part of the implementation of Jit-Lock mode, used by Font-Lock.

— Variable: fontification-functions

This variable holds a list of functions that are called by Emacs redisplay as needed, just before doing redisplay. They are called even when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this variable usually holds just one function, jit-lock-function.

The functions are called in the order listed, with one argument, a buffer position pos. Collectively they should attempt to assign faces to the text in the current buffer starting at pos.

The functions should record the faces they assign by setting the face property. They should also add a non-nil fontified property to all the text they have assigned faces to. That property tells redisplay that faces have been assigned to that text already.

It is probably a good idea for the functions to do nothing if the character after pos already has a non-nil fontified property, but this is not required. If one function overrides the assignments made by a previous one, the properties after the last function finishes are the ones that really matter.

For efficiency, we recommend writing these functions so that they usually assign faces to around 400 to 600 characters at each call.