Highlight Lua regexp meta characters

[mnacamura]

pattern	5.1	jit	5.2	5.3	5.4
^$()%.[]*+-?	x	x	x	x	x
%(any non-alphanumeric character)	x	x	x	x	x
.	x	x	x	x	x
%a	x	x	x	x	x
%c	x	x	x	x	x
%d	x	x	x	x	x
%l	x	x	x	x	x
%p	x	x	x	x	x
%s	x	x	x	x	x
%u	x	x	x	x	x
%w	x	x	x	x	x
%x	x	x	x	x	x
[set]	x	x	x	x	x
[^set]	x	x	x	x	x
%z	x	x	-	-	-
%g	-	x	x	x	x

[mnacamura]

In usual string, it should be bothersome if regexp meta characters, which are normal characters in the normal string, are highlighted. We need to highlight these meta characters only in regexp string. But how?