JavaScript currently uses an older version of the Unicode database. Here are some examples of identifiers that are currently failing because of this, even though they’re valid according to ES 5.1/Unicode 6.1: * `var \u0cf1;` — http://mothereff.in/js-variables#%5Cu0cf1 * `var \ua7aa;` — http://mothereff.in/js-variables#%5Cua7aa * `var \u1bba;` — http://mothereff.in/js-variables#%5Cu1bba * `var a\ua674;` — http://mothereff.in/js-variables#a%5Cua674 Of course, there are many more. Updating to Unicode 6.1 would improve interoperability. Is the list of allowed characters in `IdentifierStart` and `IdentifierPart` auto-generated based on a UnicodeData.txt file, or how is this done in JavaScriptCore?