Số lượng chính xác `{n,m}`

When you need precise control over the number of repetitions, you use the brace notation {n,m}:

{n} is equivalent to {n,n}. {n,} has no maximum. {,m} is not supported in JavaScript (you must write {0,m}).

Pattern: \d{4}
Sample:  Anni: 2020, 2024, 1999, errore 99.
               ^^^^  ^^^^  ^^^^

{4} stops the match at exactly four digits: 99 does not match because it has only two. 12345 would match the first four digits (1234), not the whole number.

Open intervals and repetition limits

The curly brace notation is flexible: {n} indicates exact repetition, {n,m} a closed range from n to m, while {n,} leaves the upper limit open ("at least n times"). The engine processes these efficiently, reducing the ambiguities of generic quantifiers.

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Review exercise

Additional challenge