Alist expressing beginning and end of regions not to spell check.
The alist key must be a regular expression.
Valid forms include:
(KEY) - just skip the key.
(KEY . REGEXP) - skip to the end of REGEXP. REGEXP may be string or symbol.
(KEY REGEXP) - skip to end of REGEXP. REGEXP must be a string.
(KEY FUNCTION ARGS) - FUNCTION called with ARGS returns end of region.