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#1802 — Section 7.6: Backwards compatibility and U+2E2F in `Identifier`s

• bug_id: 1802
• creation_ts: 2013-08-22 11:38:00 -0700
• short_desc: Section 7.6: Backwards compatibility and U+2E2F in `Identifier`s
• delta_ts: 2013-09-18 14:33:59 -0700
• product: Draft for 6th Edition
• component: technical issue
• version: Rev 16: July 15, 2013 Draft
• rep_platform: All
• op_sys: All
• bug_status: RESOLVED
• resolution: WORKSFORME
• bug_file_loc: http://mathiasbynens.be/demo/javascript-identifier-regex
• priority: Normal
• bug_severity: enhancement
• everconfirmed: true
• reporter: Mathias Bynens
• assigned_to: Allen Wirfs-Brock
• cc: ["annevk", "ecmascriptbugs", "mathias", "utatane.tea"]

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• commentid: 5010
• comment_count: 0
• who: Mathias Bynens
• bug_when: 2013-08-22 11:38:47 -0700

I wrote a (new) script that generates a regular expression that matches valid JavaScript identifiers as per ECMAScript 5.1 / Unicode v6.2.0. mathiasbynens.be/demo/javascript-identifier-regex

Then, I made it do the same thing according to the latest ECMAScript 6 draft, which refers to Unicode Standard Annex #31: Unicode Identifier and Pattern Syntax (www.unicode.org/reports/tr31).

After comparing the output, I noticed that both regular expressions are identical except for the following: ECMAScript 5 allows U+2E2F VERTICAL TILDE in IdentifierStart and IdentifierPart, but ECMAScript 6 / Unicode TR31 doesn’t.

Was this potentially breaking change intentional? I’m fine with disallowing U+2E2F, but only if we’re sure it doesn’t break any existing code.

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• commentid: 5401
• comment_count: 1
• who: Anne van Kesteren
• bug_when: 2013-09-18 14:33:59 -0700

We decided on Sep 17 that it was intentional. Implementations need to use the ID_Start category instead.