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Editorial: update Annex E with incompatibilities from previous editio…
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…ns (tc39#1698)

 - 2016: the Unicode change affected what was considered whitespace (tc39#300 / 24dad16)
 - 2017: the latest version of Unicode is mandated (tc39#620)
 - 2018: changed tagged template literal objects to be cached per source location rather than per realm (tc39#890)
 - 2019: Atomics.wake was renamed to Atomics.notify (tc39#1220)
 - 2019: `await` was changed to require fewer ticks (tc39#1250)
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ljharb committed Oct 18, 2019
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Expand Up @@ -42797,8 +42797,10 @@ <h1>Corrections and Clarifications in ECMAScript 2015 with Possible Compatibilit

<emu-annex id="sec-additions-and-changes-that-introduce-incompatibilities-with-prior-editions">
<h1>Additions and Changes That Introduce Incompatibilities with Prior Editions</h1>
<p><emu-xref href="#sec-tonumber-applied-to-the-string-type"></emu-xref>: In ECMAScript 2015, ToNumber applied to a String value now recognizes and converts |BinaryIntegerLiteral| and |OctalIntegerLiteral| numeric strings. In previous editions such strings were converted to *NaN*.</p>
<p><emu-xref href="#sec-reference-specification-type"></emu-xref>: In ECMAScript 2015, Function calls are not allowed to return a Reference value.</p>
<p><emu-xref href="#sec-tonumber-applied-to-the-string-type"></emu-xref>: In ECMAScript 2015, ToNumber applied to a String value now recognizes and converts |BinaryIntegerLiteral| and |OctalIntegerLiteral| numeric strings. In previous editions such strings were converted to *NaN*.</p>
<p><emu-xref href="#sec-code-realms"></emu-xref>: In ECMAScript 2018, Template objects are canonicalized based on Parse Node (source location), instead of across all occurrences of that template literal or tagged template in a Realm in previous editions.</p>
<p><emu-xref href="#sec-white-space"></emu-xref>: In ECMASCript 2016, Unicode 8.0.0 or higher is mandated, as opposed to ECMAScript 2015 which mandated Unicode 5.1. In particular, this caused U+180E MONGOLIAN VOWEL SEPARATOR, which was in the `Space_Separator` (`Zs`) category and thus treated as whitespace in ECMAScript 2015, to be moved to the `Format` (`Cf`) category (as of Unicode 6.3.0). This causes whitespace-sensitive methods to behave differently. For example, `"\u180E".trim().length` was `0` in previous editions, but `1` in ECMAScript 2016 and later. Additionally, ECMAScript 2017 mandated always using the latest version of the Unicode standard.</p>
<p><emu-xref href="#sec-names-and-keywords"></emu-xref>: In ECMAScript 2015, the valid code points for an |IdentifierName| are specified in terms of the Unicode properties &ldquo;ID_Start&rdquo; and &ldquo;ID_Continue&rdquo;. In previous editions, the valid |IdentifierName| or |Identifier| code points were specified by enumerating various Unicode code point categories.</p>
<p><emu-xref href="#sec-rules-of-automatic-semicolon-insertion"></emu-xref>: In ECMAScript 2015, Automatic Semicolon Insertion adds a semicolon at the end of a do-while statement if the semicolon is missing. This change aligns the specification with the actual behaviour of most existing implementations.</p>
<p><emu-xref href="#sec-object-initializer-static-semantics-early-errors"></emu-xref>: In ECMAScript 2015, it is no longer an early error to have duplicate property names in Object Initializers.</p>
Expand Down Expand Up @@ -42836,6 +42838,8 @@ <h1>Additions and Changes That Introduce Incompatibilities with Prior Editions</
<p><emu-xref href="#sec-regexp-pattern-flags"></emu-xref> In ECMAScript 2015, If the _pattern_ argument is a RegExp instance and the _flags_ argument is not *undefined*, a new RegExp instance is created just like _pattern_ except that _pattern_'s flags are replaced by the argument _flags_. In previous editions a *TypeError* exception was thrown when _pattern_ was a RegExp instance and _flags_ was not *undefined*.</p>
<p><emu-xref href="#sec-properties-of-the-regexp-prototype-object"></emu-xref> In ECMAScript 2015, the RegExp prototype object is not a RegExp instance. In previous editions it was a RegExp instance whose pattern is the empty string.</p>
<p><emu-xref href="#sec-properties-of-the-regexp-prototype-object"></emu-xref> In ECMAScript 2015, `"source"`, `"global"`, `"ignoreCase"`, and `"multiline"` are accessor properties defined on the RegExp prototype object. In previous editions they were data properties defined on RegExp instances.</p>
<p><emu-xref href="#sec-atomics.notify"></emu-xref>: In ECMAScript 2019, `Atomics.wake` has been renamed to `Atomics.notify` to prevent confusion with `Atomics.wait`.</p>
<p><emu-xref="#sec-asyncfromsynciteratorcontinuation"></emu-xref>, <emu-xref href="#sec-asyncgeneratorresumenext"></emu-xref>: In ECMAScript 2019, the number of Jobs enqueued by `await` was reduced, which could create an observable difference in resolution order between a `then()` call and an `await` expression.</p>
</emu-annex>
<emu-annex id="sec-colophon">
<h1>Colophon</h1>
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