ame">start</span> = <span class="default-value">0</span>, </span></li>
<li><span class="parameter" id="normalize-param-end"><span class="type-annotation"><a href="../../dart-core/int-class.html">int</a></span> <span class="parameter-name">end</span>]</span></li>
</ol>)
      
    </section>
    <section class="desc markdown">
      <p>Validates and normalizes the base64 encoded data in <code>source</code>.</p>
<p>Only acts on the substring from <code>start</code> to <code>end</code>, with <code>end</code>
d