It's simple for a single character, e.g. the "c" from the example above:
This uses negative lookbehind and lookahead to make sure the two c's are not preceeded or followed by any other c's.
@hirojin I did think of something similar, but [\1] matches character with ASCII code 1 (base 80), and not the backref. E.g. [\80] would match 0.
As far as I can tell, it's not possible to use back-references in square brackets.
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!