Backwards compatibility and U+2E2F in `Identifier`s

Mathias Bynens mathias at
Sat Aug 24 14:21:57 PDT 2013

> I had no intentions specific to U+2E2F when I proposed relying on UTR 31 - the change is simply the effect of the character properties that the Unicode Technical Committee assigned to this character.
> I don't think there's a real problem. U+2E2F was added in Unicode version 5.1. ECMAScript 5.1 requires only support for Unicode 3.0, and warns "If portability is a concern, programmers should only employ identifier characters defined in Unicode 3.0" (section 7.6). IE 10 throws a SyntaxError if the character is used in an identifier.
> BTW, if that's the only difference between the regular expressions for ES 5.1 and ES 6, then at least one of them is wrong - ES 6 allows supplementary characters in identifiers, while ES 5.1 doesn't.

It’s the only difference in the BMP range. (Like you said, differences in the astral range are to be expected, since astral symbols weren’t allowed in ES5. No back-compat issues there.)

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