title: Weird behaviour of Array index in Ruby 3.1
body: <p>I don't know why this is happening in my ruby, but do you see the same behaviour?</p>
  <pre><code>3.1.2 :001 &gt; [&quot;url&quot;, &quot;label:from&quot;, &quot;label:type&quot;, &quot;label:batch&quot;, &quot;note&quot;].index('url')
   =&gt; nil
  </code></pre>
  <pre><code>3.1.2 :002 &gt; [&quot;url&quot;, &quot;label:from&quot;, &quot;label:type&quot;, &quot;label:batch&quot;, &quot;note&quot;].index('note')
   =&gt; 4
  </code></pre>
  <pre><code>3.1.2 :003 &gt; [&quot;Url&quot;, &quot;label:from&quot;, &quot;label:type&quot;, &quot;label:batch&quot;, &quot;note&quot;].index('Url')
   =&gt; 0
  </code></pre>
  <p>It can't find 'url' when downcased. Is this a reserved word?</p>
  <p>Edit: it seems not to be able to find the first occurrence of &quot;url&quot; string:</p>
  <pre><code>[&quot;note&quot;, &quot;url&quot;, &quot;label:from&quot;, &quot;label:type&quot;, &quot;label:batch&quot;, &quot;note&quot;, &quot;url&quot;].index 'url'
   =&gt; 6       
  </code></pre>