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<title>Issue 2343: Is the value of the ECMA-262 RegExp object's multiline property really false?</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#Resolved">Resolved</a> status.</em></p>
<h3 id="2343"><a href="lwg-defects.html#2343">2343</a>. Is the value of the ECMA-262 RegExp object's multiline property really false?</h3>
<p><b>Section:</b> 28.6.12 <a href="https://wg21.link/re.grammar">[re.grammar]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Nayuta Taga <b>Opened:</b> 2013-10-30 <b>Last modified:</b> 2017-03-12</p>
<p><b>Priority: </b>2
</p>
<p><b>View other</b> <a href="lwg-index-open.html#re.grammar">active issues</a> in [re.grammar].</p>
<p><b>View all other</b> <a href="lwg-index.html#re.grammar">issues</a> in [re.grammar].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In the following "Multiline" is the value of the ECMA-262 RegExp object's multiline property.
<p/>
In <a href="http://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf">ECMA-262</a>, 
there are some definitions that relate to Multiline:
</p>
<ul>
<li><p>
ECMA-262 15.10.2.6:
</p>
<blockquote>
<p>
If Multiline is true, ^ matches just after LineTerminator.
<p/>
If Multiline is false, ^ does not match just after LineTerminator.
<p/>
If Multiline is true, $ matches just before LineTerminator.
<p/>
If Multiline is false, $ does not match just before LineTerminator.
</p>
</blockquote>
</li>
<li>
<p>
ECMA-262 15.10.4.1, 15.10.7.4:
</p>
<blockquote><p>
By default, Multiline is false.
</p></blockquote>
</li>
</ul>
<p>
So, the C++11 standard says that Multiline is false. As it is false,
^ matches only the beginning of the string, and $ matches only the end
of the string.
<p/>
However, two flags are defined in 28.6.4.3 <a href="https://wg21.link/re.matchflag">[re.matchflag]</a> Table 139:
</p>
<blockquote>
<p>
<code>match_not_bol</code>: the character ^ in the regular expression shall not match <code>[first,first)</code>.
<p/>
<code>match_not_eol</code>: the character "$" in the regular expression shall not match <code>[last,last)</code>.
</p>
</blockquote>
<p>
As Multiline is false, the <code>match_not_bol</code> and the <code>match_not_eol</code> are
meaningless because they only make ^ and $ match none.
<p/>
In my opinion, Multiline should be true.
<p/>
FYI, Multiline of the existing implementations are as follows:
<p/>
<em>Multiline=false:</em>
</p>
<ul>
<li><p>
libstdc++ r206594
</p></li>
<li><p>
libc++ r199174
</p></li>
</ul>
<p>
<em>Multiline=true:</em>
</p>
<ul>
<li><p>
Visual Studio Express 2013
</p></li>
<li><p>
boost 1.55
</p></li>
</ul>

<p><i>[2015-05-22, Daniel comments]</i></p>

<p>
This issue interacts with LWG <a href="lwg-defects.html#2503" title="multiline option should be added to syntax_option_type (Status: C++17)">2503</a><sup><a href="https://cplusplus.github.io/LWG/issue2503" title="Latest snapshot">(i)</a></sup>.
</p>

<p><i>[2016-08 Chicago]</i></p>

<p>Resolving <a href="lwg-defects.html#2503" title="multiline option should be added to syntax_option_type (Status: C++17)">2503</a><sup><a href="https://cplusplus.github.io/LWG/issue2503" title="Latest snapshot">(i)</a></sup> will resolve this as well.</p>


<p id="res-2343"><b>Proposed resolution:</b></p>
<p>Resolved by LWG <a href="lwg-defects.html#2503" title="multiline option should be added to syntax_option_type (Status: C++17)">2503</a><sup><a href="https://cplusplus.github.io/LWG/issue2503" title="Latest snapshot">(i)</a></sup>.</p>





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