Erik Corry wrote:
[...snip] what does /[^\0-\uFFFF\u{10000}]/ without /u match?
Without the /u flag it should behave exactly as it has done until now,
for reasons of backwards
compatibility. On V8 that means that
/[\u{10000}]/
is the same as
/[u01{}]/
That sounds good. Not only does it avoid breaking from web-reality, it also
means that regexes without /u don't need to use a weird mix of code unit and
code point matching semantics, ever. To extend the backward compatible
approach you prescribe here, the following should all be true when /u is not
used:
* /\u{10}/ eq /u{10}/ (literal u repeated 10 times).
* Shorthand classes like \D, \S, and the dot match BMP code units only.
* [^\0-\uFFFF] eq [] eq (?!) eq \b\B. (All of these are used in real-world
regexes.)
* If ES6 or later adds \p{..} for Unicode property matching, it's limited to
matching BMP code units.
In other words, without /u, all matching is restricted to BMP code units.
With /u, all matching is code point based and works with full 21-bit
Unicode.
This also provides another argument in favor of automatically implying /u in
ES modules. It would be somewhat obnoxious to not let \u{..} work by default
in modules.
-- Steven Levithan
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