Function: jit-lock-after-change

Mark the rest of the buffer as not fontified after a change.
Installed on `after-change-functions'.
START and END are the start and end of the changed text. OLD-LEN
is the pre-change length.
This function ensures that lines following the change will be refontified
in case the syntax of those lines has changed. Refontification
will take place when text is fontified stealthily.