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Editorial: Improve specification of [RegExp]IdentifierNames #2392

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ljharb merged 3 commits into from
Sep 28, 2021
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Editorial: Improve specification of [RegExp]IdentifierNames #2392

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a50d274
Editorial: Introduce `IdentifierStartChar` + `IdentifierPartChar` (#2…
jmdyck Sep 28, 2021
6d2ba3c
Editorial: Introduce [RegExp]IdentifierCodePoint[s] SDOs (#2392)
jmdyck Sep 28, 2021
1901514
Editorial: Move 2 paragraphs down one level (#2392)
jmdyck Sep 28, 2021
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145 changes: 112 additions & 33 deletions spec.html
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Expand Up @@ -16163,8 +16163,6 @@ <h1>Names and Keywords</h1>
<emu-note>
<p>This standard specifies specific code point additions: U+0024 (DOLLAR SIGN) and U+005F (LOW LINE) are permitted anywhere in an |IdentifierName|, and the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D (ZERO WIDTH JOINER) are permitted anywhere after the first code point of an |IdentifierName|.</p>
</emu-note>
<p>Unicode escape sequences are permitted in an |IdentifierName|, where they contribute a single Unicode code point to the |IdentifierName|. The code point is expressed by the |CodePoint| of the |UnicodeEscapeSequence| (see <emu-xref href="#sec-literals-string-literals"></emu-xref>). The `\\` preceding the |UnicodeEscapeSequence| and the `u` and `{ }` code units, if they appear, do not contribute code points to the |IdentifierName|. A |UnicodeEscapeSequence| cannot be used to put a code point into an |IdentifierName| that would otherwise be illegal. In other words, if a `\\` |UnicodeEscapeSequence| sequence were replaced by the |SourceCharacter| it contributes, the result must still be a valid |IdentifierName| that has the exact same sequence of |SourceCharacter| elements as the original |IdentifierName|. All interpretations of |IdentifierName| within this specification are based upon their actual code points regardless of whether or not an escape sequence was used to contribute any particular code point.</p>
<p>Two |IdentifierName|s that are canonically equivalent according to the Unicode standard are <em>not</em> equal unless, after replacement of each |UnicodeEscapeSequence|, they are represented by the exact same sequence of code points.</p>
<h2>Syntax</h2>
<emu-grammar type="definition">
PrivateIdentifier ::
Expand All @@ -16175,15 +16173,21 @@ <h2>Syntax</h2>
IdentifierName IdentifierPart

IdentifierStart ::
IdentifierStartChar
`\` UnicodeEscapeSequence

IdentifierPart ::
IdentifierPartChar
`\` UnicodeEscapeSequence

IdentifierStartChar ::
UnicodeIDStart
`$`
`_`
`\` UnicodeEscapeSequence

IdentifierPart ::
IdentifierPartChar ::
UnicodeIDContinue
`$`
`\` UnicodeEscapeSequence
&lt;ZWNJ&gt;
&lt;ZWJ&gt;

Expand All @@ -16203,22 +16207,63 @@ <h2>Syntax</h2>

<emu-clause id="sec-identifier-names">
<h1>Identifier Names</h1>
<p>Unicode escape sequences are permitted in an |IdentifierName|, where they contribute a single Unicode code point to the |IdentifierName|. The code point is expressed by the |CodePoint| of the |UnicodeEscapeSequence| (see <emu-xref href="#sec-literals-string-literals"></emu-xref>). The `\\` preceding the |UnicodeEscapeSequence| and the `u` and `{ }` code units, if they appear, do not contribute code points to the |IdentifierName|. A |UnicodeEscapeSequence| cannot be used to put a code point into an |IdentifierName| that would otherwise be illegal. In other words, if a `\\` |UnicodeEscapeSequence| sequence were replaced by the |SourceCharacter| it contributes, the result must still be a valid |IdentifierName| that has the exact same sequence of |SourceCharacter| elements as the original |IdentifierName|. All interpretations of |IdentifierName| within this specification are based upon their actual code points regardless of whether or not an escape sequence was used to contribute any particular code point.</p>
<p>Two |IdentifierName|s that are canonically equivalent according to the Unicode standard are <em>not</em> equal unless, after replacement of each |UnicodeEscapeSequence|, they are represented by the exact same sequence of code points.</p>

<emu-clause id="sec-identifier-names-static-semantics-early-errors">
<h1>Static Semantics: Early Errors</h1>
<emu-grammar>IdentifierStart :: `\` UnicodeEscapeSequence</emu-grammar>
<ul>
<li>
It is a Syntax Error if the SV of |UnicodeEscapeSequence| is none of *"$"*, or *"_"*, or ! UTF16EncodeCodePoint(_cp_) for some Unicode code point _cp_ matched by the |UnicodeIDStart| lexical grammar production.
It is a Syntax Error if IdentifierCodePoint of |UnicodeEscapeSequence| is not some Unicode code point matched by the |IdentifierStartChar| lexical grammar production.
</li>
</ul>
<emu-grammar>IdentifierPart :: `\` UnicodeEscapeSequence</emu-grammar>
<ul>
<li>
It is a Syntax Error if the SV of |UnicodeEscapeSequence| is none of *"$"*, *"_"*, ! UTF16EncodeCodePoint(&lt;ZWNJ&gt;), ! UTF16EncodeCodePoint(&lt;ZWJ&gt;), or ! UTF16EncodeCodePoint(_cp_) for some Unicode code point _cp_ that would be matched by the |UnicodeIDContinue| lexical grammar production.
It is a Syntax Error if IdentifierCodePoint of |UnicodeEscapeSequence| is not some Unicode code point matched by the |IdentifierPartChar| lexical grammar production.
</li>
</ul>
</emu-clause>

<emu-clause id="sec-identifiercodepoints" type="sdo">
<h1>Static Semantics: IdentifierCodePoints</h1>
<dl class="header">
</dl>
<emu-grammar>IdentifierName :: IdentifierStart</emu-grammar>
<emu-alg>
1. Let _cp_ be IdentifierCodePoint of |IdentifierStart|.
1. Return &laquo; _cp_ &raquo;.
</emu-alg>
<emu-grammar>IdentifierName :: IdentifierName IdentifierPart</emu-grammar>
<emu-alg>
1. Let _cps_ be IdentifierCodePoints of the derived |IdentifierName|.
1. Let _cp_ be IdentifierCodePoint of |IdentifierPart|.
1. Return the list-concatenation of _cps_ and &laquo; _cp_ &raquo;.
</emu-alg>
</emu-clause>

<emu-clause id="sec-identifiercodepoint" type="sdo">
<h1>Static Semantics: IdentifierCodePoint</h1>
<dl class="header">
</dl>
<emu-grammar>IdentifierStart :: IdentifierStartChar</emu-grammar>
<emu-alg>
1. Return the code point matched by |IdentifierStartChar|.
</emu-alg>
<emu-grammar>IdentifierPart :: IdentifierPartChar</emu-grammar>
<emu-alg>
1. Return the code point matched by |IdentifierPartChar|.
</emu-alg>
<emu-grammar>UnicodeEscapeSequence :: `u` Hex4Digits</emu-grammar>
<emu-alg>
1. Return the code point whose numeric value is the MV of |Hex4Digits|.
</emu-alg>
<emu-grammar>UnicodeEscapeSequence :: `u{` CodePoint `}`</emu-grammar>
<emu-alg>
1. Return the code point whose numeric value is the MV of |CodePoint|.
</emu-alg>
</emu-clause>
</emu-clause>

<emu-clause id="sec-keywords-and-reserved-words" oldids="sec-reserved-words,sec-keywords,sec-future-reserved-words">
Expand Down Expand Up @@ -17057,22 +17102,12 @@ <h2>Syntax</h2>

RegularExpressionFlags ::
[empty]
RegularExpressionFlags IdentifierPart
RegularExpressionFlags IdentifierPartChar
</emu-grammar>
<emu-note>
<p>Regular expression literals may not be empty; instead of representing an empty regular expression literal, the code unit sequence `//` starts a single-line comment. To specify an empty regular expression, use: `/(?:)/`.</p>
</emu-note>

<emu-clause id="sec-literals-regular-expression-literals-static-semantics-early-errors">
<h1>Static Semantics: Early Errors</h1>
<emu-grammar>RegularExpressionFlags :: RegularExpressionFlags IdentifierPart</emu-grammar>
<ul>
<li>
It is a Syntax Error if |IdentifierPart| contains a Unicode escape sequence.
</li>
</ul>
</emu-clause>

<emu-clause id="sec-static-semantics-bodytext" type="sdo">
<h1>Static Semantics: BodyText</h1>
<dl class="header">
Expand Down Expand Up @@ -17676,8 +17711,7 @@ <h1>Static Semantics: StringValue</h1>
IdentifierName IdentifierPart
</emu-grammar>
<emu-alg>
1. Let _idText_ be the source text matched by |IdentifierName|.
1. Let _idTextUnescaped_ be the result of replacing any occurrences of `\\` |UnicodeEscapeSequence| in _idText_ with the code point represented by the |UnicodeEscapeSequence|.
1. Let _idTextUnescaped_ be IdentifierCodePoints of |IdentifierName|.
1. Return ! CodePointsToString(_idTextUnescaped_).
</emu-alg>
<emu-grammar>
Expand Down Expand Up @@ -34244,19 +34278,14 @@ <h2>Syntax</h2>
RegExpIdentifierName[?UnicodeMode] RegExpIdentifierPart[?UnicodeMode]

RegExpIdentifierStart[UnicodeMode] ::
UnicodeIDStart
`$`
`_`
IdentifierStartChar
`\` RegExpUnicodeEscapeSequence[+UnicodeMode]
[~UnicodeMode] UnicodeLeadSurrogate UnicodeTrailSurrogate

RegExpIdentifierPart[UnicodeMode] ::
UnicodeIDContinue
`$`
IdentifierPartChar
`\` RegExpUnicodeEscapeSequence[+UnicodeMode]
[~UnicodeMode] UnicodeLeadSurrogate UnicodeTrailSurrogate
&lt;ZWNJ&gt;
&lt;ZWJ&gt;

RegExpUnicodeEscapeSequence[UnicodeMode] ::
[+UnicodeMode] `u` HexLeadSurrogate `\u` HexTrailSurrogate
Expand Down Expand Up @@ -34418,25 +34447,25 @@ <h1>Static Semantics: Early Errors</h1>
<emu-grammar>RegExpIdentifierStart :: `\` RegExpUnicodeEscapeSequence</emu-grammar>
<ul>
<li>
It is a Syntax Error if the CharacterValue of |RegExpUnicodeEscapeSequence| is not the code point value of *"$"*, *"_"*, or some code point matched by the |UnicodeIDStart| lexical grammar production.
It is a Syntax Error if the CharacterValue of |RegExpUnicodeEscapeSequence| is not the code point value of some code point matched by the |IdentifierStartChar| lexical grammar production.
</li>
</ul>
<emu-grammar>RegExpIdentifierStart :: UnicodeLeadSurrogate UnicodeTrailSurrogate</emu-grammar>
<ul>
<li>
It is a Syntax Error if the result of performing UTF16SurrogatePairToCodePoint on the two code points matched by |UnicodeLeadSurrogate| and |UnicodeTrailSurrogate| respectively is not matched by the |UnicodeIDStart| lexical grammar production.
It is a Syntax Error if RegExpIdentifierCodePoint of |RegExpIdentifierStart| is not matched by the |UnicodeIDStart| lexical grammar production.
</li>
</ul>
<emu-grammar>RegExpIdentifierPart :: `\` RegExpUnicodeEscapeSequence</emu-grammar>
<ul>
<li>
It is a Syntax Error if the CharacterValue of |RegExpUnicodeEscapeSequence| is not the code point value of *"$"*, *"_"*, &lt;ZWNJ&gt;, &lt;ZWJ&gt;, or some code point matched by the |UnicodeIDContinue| lexical grammar production.
It is a Syntax Error if the CharacterValue of |RegExpUnicodeEscapeSequence| is not the code point value of some code point matched by the |IdentifierPartChar| lexical grammar production.
</li>
</ul>
<emu-grammar>RegExpIdentifierPart :: UnicodeLeadSurrogate UnicodeTrailSurrogate</emu-grammar>
<ul>
<li>
It is a Syntax Error if the result of performing UTF16SurrogatePairToCodePoint on the two code points matched by |UnicodeLeadSurrogate| and |UnicodeTrailSurrogate| respectively is not matched by the |UnicodeIDContinue| lexical grammar production.
It is a Syntax Error if RegExpIdentifierCodePoint of |RegExpIdentifierPart| is not matched by the |UnicodeIDContinue| lexical grammar production.
</li>
</ul>
<emu-grammar>UnicodePropertyValueExpression :: UnicodePropertyName `=` UnicodePropertyValue</emu-grammar>
Expand Down Expand Up @@ -34719,11 +34748,59 @@ <h1>Static Semantics: CapturingGroupName</h1>
RegExpIdentifierName RegExpIdentifierPart
</emu-grammar>
<emu-alg>
1. Let _idText_ be the source text matched by |RegExpIdentifierName|.
1. Let _idTextUnescaped_ be the result of replacing any occurrences of `\\` |RegExpUnicodeEscapeSequence| in _idText_ with the code point represented by the |RegExpUnicodeEscapeSequence|.
1. Let _idTextUnescaped_ be RegExpIdentifierCodePoints of |RegExpIdentifierName|.
1. Return ! CodePointsToString(_idTextUnescaped_).
</emu-alg>
</emu-clause>

<emu-clause id="sec-regexpidentifiercodepoints" type="sdo">
<h1>Static Semantics: RegExpIdentifierCodePoints</h1>
<dl class="header">
</dl>
<emu-grammar>RegExpIdentifierName :: RegExpIdentifierStart</emu-grammar>
<emu-alg>
1. Let _cp_ be RegExpIdentifierCodePoint of |RegExpIdentifierStart|.
1. Return &laquo; _cp_ &raquo;.
</emu-alg>
<emu-grammar>RegExpIdentifierName :: RegExpIdentifierName RegExpIdentifierPart</emu-grammar>
<emu-alg>
1. Let _cps_ be RegExpIdentifierCodePoints of the derived |RegExpIdentifierName|.
1. Let _cp_ be RegExpIdentifierCodePoint of |RegExpIdentifierPart|.
1. Return the list-concatenation of _cps_ and &laquo; _cp_ &raquo;.
</emu-alg>
</emu-clause>

<emu-clause id="sec-regexpidentifiercodepoint" type="sdo">
<h1>Static Semantics: RegExpIdentifierCodePoint</h1>
<dl class="header">
</dl>
<emu-grammar>RegExpIdentifierStart :: IdentifierStartChar</emu-grammar>
<emu-alg>
1. Return the code point matched by |IdentifierStartChar|.
</emu-alg>
<emu-grammar>RegExpIdentifierPart :: IdentifierPartChar</emu-grammar>
<emu-alg>
1. Return the code point matched by |IdentifierPartChar|.
</emu-alg>
<emu-grammar>
RegExpIdentifierStart :: `\` RegExpUnicodeEscapeSequence

RegExpIdentifierPart :: `\` RegExpUnicodeEscapeSequence
</emu-grammar>
<emu-alg>
1. Return the code point whose numeric value is the CharacterValue of |RegExpUnicodeEscapeSequence|.
</emu-alg>
<emu-grammar>
RegExpIdentifierStart :: UnicodeLeadSurrogate UnicodeTrailSurrogate

RegExpIdentifierPart :: UnicodeLeadSurrogate UnicodeTrailSurrogate
</emu-grammar>
<emu-alg>
1. Let _lead_ be the code unit whose numeric value is that of the code point matched by |UnicodeLeadSurrogate|.
1. Let _trail_ be the code unit whose numeric value is that of the code point matched by |UnicodeTrailSurrogate|.
1. Return UTF16SurrogatePairToCodePoint(_lead_, _trail_).
</emu-alg>
</emu-clause>
</emu-clause>

<emu-clause id="sec-pattern-semantics">
Expand Down Expand Up @@ -46020,6 +46097,8 @@ <h1>Lexical Grammar</h1>
<emu-prodref name="IdentifierName"></emu-prodref>
<emu-prodref name="IdentifierStart"></emu-prodref>
<emu-prodref name="IdentifierPart"></emu-prodref>
<emu-prodref name="IdentifierStartChar"></emu-prodref>
<emu-prodref name="IdentifierPartChar"></emu-prodref>
<emu-prodref name="UnicodeIDStart"></emu-prodref>
<emu-prodref name="UnicodeIDContinue"></emu-prodref>
<emu-prodref name="ReservedWord"></emu-prodref>
Expand Down