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

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.

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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 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 *).

Issue でリンクされている「Lookahead and lookbehind」の記事から始め、特に lookahead と lookbehind のセクションを確認してください。記載されている例を、lookbehind 式における固定長でないパターンに対する JavaScript の制限と比較してください。記事がその制限を明確に説明し、lookahead の動作と lookbehind の動作を区別できていれば完了です。