Non-capturing group, recursion and OR operands, PHP regex

PHP Regex code:

(?: [^[] | [ (?! /?indent] ) | (?R) )

- (?: ...) - this is a non-capturing group, the whole thing here
- (?! ...) - negative lookahead. Specifies a group that cannot match after the main expression (if it matches the result is discarded)
- (?R) - recursion

I am at the beginning of leaing the regex and I am not understanding how this works as a whole. I guess I am not understanding some aspects like the OR operator or the recursion part?

a) How does the recursion work in the context of (?: A | B | (?R) )
b) Is OR, in general, behaving like this "if A matches I dont go to B?", and again the (?R) part in this context.

Thanks!