Advance to stage 4

[domenic]

Criteria:

• Those from stage 3

This is #12.

• Test 262 acceptance tests have been written for mainline usage scenarios.

This is #1.

• Two compatible implementations which pass the acceptance tests.

This requires completion of two out of #7, #8, #9 plus also #27 and #28.

• The ECMAScript editor has signed off on the current spec text.

This seems like a dupe of a requirement from stage 3. In any case, tracked as #11.

Implementation types expected during this stage:

• Shipping

This requires completion of two out of #7, #8, #9 plus also #27 and #28.

Finally:

• Get TC39 to agree that we have advanced to stage 4, after meeting all the above requirements.