Info Catalog elisp: Font Lock Multiline elisp: Multiline Font Lock

elisp: Region to Refontify

 
 22.6.9.2 Region to Fontify after a Buffer Change
 ................................................
 
 When a buffer is changed, the region that Font Lock refontifies is by
 default the smallest sequence of whole lines that spans the change.
 While this works well most of the time, sometimes it doesn’t—for
 example, when a change alters the syntactic meaning of text on an
 earlier line.
 
    You can enlarge (or even reduce) the region to refontify by setting
 the following variable:
 
  -- Variable: font-lock-extend-after-change-region-function
      This buffer-local variable is either ‘nil’ or a function for Font
      Lock mode to call to determine the region to scan and fontify.
 
      The function is given three parameters, the standard BEG, END, and
      OLD-LEN from ‘after-change-functions’ (Change Hooks).  It
      should return either a cons of the beginning and end buffer
      positions (in that order) of the region to fontify, or ‘nil’ (which
      means choose the region in the standard way).  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.
 

Info Catalog elisp: Font Lock Multiline elisp: Multiline Font Lock