Advance to stage 4

[mathiasbynens]

Criteria taken from the TC39 process document minus those from previous stages:

• Test262 acceptance tests have been written for mainline usage scenarios, and merged

tc39/test262#997 (thanks to @littledan and @schuay)

• Two compatible implementations which pass the acceptance tests

https://github.com/tc39/proposal-regexp-dotall-flag#implementations

Bug tickets to track:

• Chrome/V8: https://bugs.chromium.org/p/v8/issues/detail?id=6172
• Edge/Chakra: RegExp: Implement dotall (/s) flag chakra-core/ChakraCore#2787
• Firefox/SpiderMonkey: https://bugzilla.mozilla.org/show_bug.cgi?id=1361856
• Safari/JavaScriptCore: https://bugs.webkit.org/show_bug.cgi?id=172634

• Significant in-the-field experience with shipping implementations, such as that provided by two independent VMs

https://github.com/tc39/proposal-regexp-dotall-flag#implementations

• A pull request has been sent to https://github.com/tc39/ecma262 with the integrated spec text

tc39/ecma262#1028

• The ECMAScript editor has signed off on the pull request

tc39/ecma262@d978ed1

[mathiasbynens]

This proposal advanced to Stage 4 at the November 28 TC39 meeting, pending ECMAScript editor sign-off on the PR. 🎉