gistfile1.txt

As of Firefox 78, we will ship an updated version of the regexp engine, which will support dotAll, unicode property escapes, and lookbehind assertions.

Use case:

 The dotAll flag allows `.` in regular expressions to match any character, including newlines.

 Unicode property escapes can be used to match characters according to certain Unicode properties. For example, `/^\p{Decimal_Number}+$/u.test('𝟏𝟐𝟑𝟜𝟝𝟞𝟩𝟪𝟫𝟬𝟭𝟮𝟯𝟺𝟻𝟼') === true`.

 Lookbehind assertions can be used to make sure that a pattern is or is not preceded by another (just as lookahead assertions can be used to make that a pattern is or is not succeeded by another).

 All three of these features were added to the standard in ES2018. They are becoming a webcompat issue. It is important to get them landed in time for ESR78.

Bug: 
 Meta bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1367105
 Bug to enable by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1634135

Standard:
 https://github.com/tc39/proposal-regexp-dotall-flag
 https://github.com/tc39/proposal-regexp-unicode-property-escapes
 https://github.com/tc39/proposal-regexp-lookbehind

Platform coverage: 
 All, no pref

DevTools bug: 
 N/A

Other browsers: 
 dotAll: 
  V8 shipping in 62 <https://bugs.chromium.org/p/v8/issues/detail?id=6172>
  JSC shipping in Safari Technology Preview 39a <https://bugs.webkit.org/show_bug.cgi?id=172634>

 Unicode property escapes:
  V8 shipping in 64 <https://bugs.chromium.org/p/v8/issues/detail?id=4743>
  JSC shipping in Safari Technology Preview 42 <https://developer.apple.com/safari/technology-preview/release-notes/>
 
 Lookbehind assertions:
  V8 shipping in 62 <https://bugs.chromium.org/p/v8/issues/detail?id=4545>
  JSC tracking issue: https://bugs.webkit.org/show_bug.cgi?id=174931
 
Testing: 
 There are test262 tests covering these features: 
  https://github.com/tc39/test262/tree/master/test/built-ins/RegExp/lookBehind
  https://github.com/tc39/test262/tree/master/test/built-ins/RegExp/dotall
  https://github.com/tc39/test262/tree/master/test/built-ins/RegExp/property-escapes

Secure contexts: 
 This is a JS language feature and is therefore present in all contexts.