Finds the absolute character index of the specified regex match
        start and end indices in the *buffer* refstring.

def absolute_charindex(self, string, start, end):
        """Finds the absolute character index of the specified regex match
        start and end indices in the *buffer* refstring."""
        search = string[start:end]
        abs_start = self.refstring.index(search)
        return abs_start, (end - start) + abs_start