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Editorial: Add notes about the 1-based indexing of regular expression _captures_ #2150

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Editorial: Add notes about the 1-based indexing of regular expression _captures_ #2150

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Editorial: Add notes about the 1-based indexing of regular expression…
gibson042 Aug 4, 2020
5e494e3
Editorial: Replace "nth element" with "element at index n"
gibson042 Aug 20, 2020
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11 changes: 8 additions & 3 deletions spec.html
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Expand Up @@ -31960,7 +31960,7 @@ <h1>Notation</h1>
A <em>CharSet</em> is a mathematical set of characters, either code units or code points depending up the state of the _Unicode_ flag. &ldquo;All characters&rdquo; means either all code unit values or all code point values also depending upon the state of _Unicode_.
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A <em>State</em> is an ordered pair (_endIndex_, _captures_) where _endIndex_ is an integer and _captures_ is a List of _NcapturingParens_ values. States are used to represent partial match states in the regular expression matching algorithms. The _endIndex_ is one plus the index of the last input character matched so far by the pattern, while _captures_ holds the results of capturing parentheses. The _n_<sup>th</sup> element of _captures_ is either a List that represents the value obtained by the _n_<sup>th</sup> set of capturing parentheses or *undefined* if the _n_<sup>th</sup> set of capturing parentheses hasn't been reached yet. Due to backtracking, many States may be in use at any time during the matching process.
A <em>State</em> is an ordered pair (_endIndex_, _captures_) where _endIndex_ is an integer and _captures_ is a List of length _NcapturingParens_, indexed 1 through _NcapturingParens_. States are used to represent partial match states in the regular expression matching algorithms. The _endIndex_ is one plus the index of the last input character matched so far by the pattern, while _captures_ holds the results of capturing parentheses. The element of _captures_ at index _n_ is either a List of characters that represents the value obtained by the _n_<sup>th</sup> set of capturing parentheses or *undefined* if the _n_<sup>th</sup> set of capturing parentheses hasn't been reached yet. Due to backtracking, many States may be in use at any time during the matching process.
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A <em>MatchResult</em> is either a State or the special token ~failure~ that indicates that the match failed.
Expand Down Expand Up @@ -32105,6 +32105,7 @@ <h1>Runtime Semantics: RepeatMatcher ( _m_, _min_, _max_, _greedy_, _x_, _c_, _p
1. If _max_ is &infin;, let _max2_ be &infin;; otherwise let _max2_ be _max_ - 1.
1. Call RepeatMatcher(_m_, _min2_, _max2_, _greedy_, _y_, _c_, _parenIndex_, _parenCount_) and return its result.
1. Let _cap_ be a copy of _x_'s _captures_ List.
1. NOTE: _cap_ is indexed from 1 (<emu-xref href="#sec-notation"></emu-xref>).
1. [id="step-repeatmatcher-clear-captures"] For each integer _k_ that satisfies _parenIndex_ &lt; _k_ and _k_ &le; _parenIndex_ + _parenCount_, set _cap_[_k_] to *undefined*.
1. Let _e_ be _x_'s _endIndex_.
1. Let _xr_ be the State (_e_, _cap_).
Expand Down Expand Up @@ -32602,6 +32603,7 @@ <h1>Atom</h1>
1. Let _d_ be a new Continuation with parameters (_y_) that captures _x_, _c_, _direction_, and _parenIndex_ and performs the following steps when called:
1. Assert: _y_ is a State.
1. Let _cap_ be a copy of _y_'s _captures_ List.
1. NOTE: _cap_ is indexed from 1 (<emu-xref href="#sec-notation"></emu-xref>).
1. Let _xe_ be _x_'s _endIndex_.
1. Let _ye_ be _y_'s _endIndex_.
1. If _direction_ is equal to +1, then
Expand Down Expand Up @@ -32767,6 +32769,7 @@ <h1>Runtime Semantics: BackreferenceMatcher ( _n_, _direction_ )</h1>
1. Assert: _x_ is a State.
1. Assert: _c_ is a Continuation.
1. Let _cap_ be _x_'s _captures_ List.
1. NOTE: _cap_ is indexed from 1 (<emu-xref href="#sec-notation"></emu-xref>).
1. Let _s_ be _cap_[_n_].
1. If _s_ is *undefined*, return _c_(_x_).
1. Let _e_ be _x_'s _endIndex_.
Expand Down Expand Up @@ -33234,7 +33237,9 @@ <h1>Runtime Semantics: RegExpBuiltinExec ( _R_, _S_ )</h1>
1. Set _e_ to _eUTF_.
1. If _global_ is *true* or _sticky_ is *true*, then
1. Perform ? Set(_R_, *"lastIndex"*, _e_, *true*).
1. Let _n_ be the number of elements in _r_'s _captures_ List. (This is the same value as <emu-xref href="#sec-notation"></emu-xref>'s _NcapturingParens_.)
1. Let _cap_ be _r_'s _captures_ List.
1. NOTE: _cap_ is indexed from 1 (<emu-xref href="#sec-notation"></emu-xref>).
1. Let _n_ be the number of elements in _cap_. (This is the same value as <emu-xref href="#sec-notation"></emu-xref>'s _NcapturingParens_.)
1. Assert: _n_ &lt; 2<sup>32</sup> - 1.
1. Let _A_ be ! ArrayCreate(_n_ + 1).
1. Assert: The value of _A_'s *"length"* property is _n_ + 1.
Expand All @@ -33248,7 +33253,7 @@ <h1>Runtime Semantics: RegExpBuiltinExec ( _R_, _S_ )</h1>
1. Let _groups_ be *undefined*.
1. Perform ! CreateDataPropertyOrThrow(_A_, *"groups"*, _groups_).
1. For each integer _i_ such that _i_ &gt; 0 and _i_ &le; _n_, do
1. Let _captureI_ be _i_<sup>th</sup> element of _r_'s _captures_ List.
1. Let _captureI_ be _cap_[_i_].
1. If _captureI_ is *undefined*, let _capturedValue_ be *undefined*.
1. Else if _fullUnicode_ is *true*, then
1. Assert: _captureI_ is a List of code points.
Expand Down