I can think of two cases: first, a character class might contain a variable with as few as one character in it (/[$foo]/); second, under the /x modifier, it's a common way to indicate a literal space (/ foo [ ] bar /x).
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In reply to Re: Why would one want in a regex a class with only a single entry? by ysth
in thread Why would one want in a regex a class with only a single entry? by ack

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