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

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[Part 3 (Additional articles)](https://javascript.info/#tab-3)
[Chapter 7 (Regular expressions)](https://javascript.info/regular-expressions)
[Article 14 (Lookahead and lookbehind)](https://javascript.info/regexp-lookahead-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](https://javascript.info/regexp-lookahead-lookbehind#lookahead), and using regexp with quantifier as lookahead condition in your example.

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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](https://javascript.info/regexp-lookahead-lookbehind#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 **\***).

Comece pelo artigo “Lookahead and lookbehind” vinculado na issue, especialmente pelas seções sobre lookahead e lookbehind. Compare os exemplos documentados com as restrições do JavaScript sobre padrões de comprimento não fixo em expressões lookbehind. O trabalho estará concluído quando o artigo explicar claramente a limitação e distinguir o comportamento de lookahead do comportamento de lookbehind.

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