Lack of essential detail about regexp lookbehind syntax in "Lookahead and lookbehind" article

[rafayel23]

Part 3 (Additional articles)
Chapter 7 (Regular expressions)
Article 14 (Lookahead and lookbehind)

Why you don't mention that in JS non fixed length regexps (including quantifiers, backreferences etc.) are not allowed inside lookbehind expression ?

First you talk about lookahead, and using regexp with quantifier as lookahead condition in your example.

Copied from www.javascript.info
For example, \d+(?=\s)(?=.*30) looks for \d+ that is followed by a space (?=\s), and there’s 30 somewhere after it (?=.\*30)

Right after this you briefly talk about lookbehind and say it is the same thing but looks behind, without mentioning that it actually cannot do the same thing with non fixed lenght regular expressions (including quantifiers like *).

[vsemozhetbyt]

As far as I know, JS does supports non fixed length regular expressions in lookbehind:

[joaquinelio]

Isn't it a browser support issue?