title: Using HTML5 form validation, can I make an input field required only if a specific <option> from a <select> menu is selected?
body: <p>Here's a simple form I have:</p>
  
  <pre><code>&lt;form name="form_1"&gt;
    &lt;fieldset&gt;
      &lt;select required name="choice"&gt;
        &lt;option value="1"&gt;Choice 1&lt;/option&gt;
        &lt;option value="2"&gt;Choice 2&lt;/option&gt;
        &lt;option value="Other"&gt;Other&lt;/option&gt;
      &lt;/select&gt;
      &lt;label for="other_text"&gt;If other, please specify: &lt;/label&gt;
      &lt;input id="other_text" name="other_text" size="30"&gt;
    &lt;/fieldset&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>How do I make the <code>"other_text"</code> input field <code>required</code> if, and only if, the <code>"choice"</code> selection is set to value <code>"Other"</code>? By default, the input field should not be required. Could this be done with only HTML5, or is Javascript required?</p>