Member predicate RegExp :: char_set_delimiter
Helper predicate for chars that could be character-set delimiters.
Holds if the (non-escaped) char at pos in the string, is the (one-based) index occurrence of a bracket ([ or ]) in the string.
Result if true is the char is [, and false if the char is ].
boolean
char_set_delimiter
(
int
index
,
int
pos
)