 padding if necessary and possible.</li>
<li>Validate that the length is correct (a multiple of four).</li>
</ul>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span></h2>
      <pre class="language-dart"><code class="language-dart">String normalize(String source, [int start = 0, int end]) {
  end = RangeError.checkValidRange(start, end, source.length);
  const percent = 0x25;
  const equals = 0x3d;
  StringBuffer buffer;
  var sliceStart = start;
 