<p></p>
<blockquote>
<p dir="auto">It's not something we need to implement - it's already implemented by the lexer.</p>
</blockquote>
<p dir="auto">To be exact, underscores denote an <em>unused</em> variable (called a "singleton"). The lexer <a href="https://github.com/ScintillaOrg/lexilla/blob/b7b401a2b169aa58dffa96888aca96b38c292a3c/lexers/LexVisualProlog.cxx#L431-L432">maps them</a> to <code class="notranslate">SCE_VISUALPROLOG_ANONYMOUS</code>:</p>
<div class="highlight highlight-source-c++"><pre>  } <span class="pl-k">else</span> <span class="pl-k">if</span> (sc.Match(<span class="pl-s"><span class="pl-pds">'</span>_<span class="pl-pds">'</span></span>)) {
      sc.<span class="pl-c1">SetState</span>(SCE_VISUALPROLOG_ANONYMOUS);</pre></div>
<p dir="auto">Only words in proper title-case <a href="https://github.com/ScintillaOrg/lexilla/blob/b7b401a2b169aa58dffa96888aca96b38c292a3c/lexers/LexVisualProlog.cxx#L429-L430">are styled</a> as <code class="notranslate">SCE_VISUALPROLOG_VARIABLE</code>:</p>
<div class="highlight highlight-source-c++"><pre>  } <span class="pl-k">else</span> <span class="pl-k">if</span> (isUpperLetter(sc.ch)) {
      sc.<span class="pl-c1">SetState</span>(SCE_VISUALPROLOG_VARIABLE);</pre></div>
<p dir="auto"><a target="_blank" rel="noopener noreferrer" href="https://user-images.githubusercontent.com/59004801/165650011-e7d48c7f-b1b7-4c5b-888d-746c49d6d18b.png"><img src="https://user-images.githubusercontent.com/59004801/165650011-e7d48c7f-b1b7-4c5b-888d-746c49d6d18b.png" alt="vpl-singleton" style="max-width: 100%;"></a></p>

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