title: Validate text that are missing terms
body: <p>I have a <code>&lt;form&gt;</code> where the user can <strong>only remove words</strong> from the input, something like:</p>
  
  <pre><code>&lt;input type="text" value="hello world 進撃進撃 lorem ipsum" name="so"&gt;
  </code></pre>
  
  <p>When I process the form, I want to ensure that the user only removed the words and didn't add their own terms etc. </p>
  
  <p>So when processing the form, I have the original value:</p>
  
  <pre><code>$original_value = 'hello world 進撃進撃 lorem ipsum';
  </code></pre>
  
  <p>And the user edited value:</p>
  
  <pre><code>$edited_value = $_POST['so'];
  </code></pre>
  
  <p>How do I validate this?</p>
  
  <h1>What I've tried so far</h1>
  
  <ul>
  <li><p>I can <code>expode()</code> the value into <em>words</em> and then cross check if the words in <code>$edited_value</code> exists in <code>$original_value</code>. </p></li>
  <li><p>I can check if all characters users in <code>$edited_value</code> exist in <code>$original_value</code> but that's a weak validation. </p></li>
  </ul>