<p>The vowels are <code>'a'</code>, <code>'e'</code>, <code>'i'</code>, <code>'o'</code>, and <code>'u'</code>, and they can appear in both lower and upper cases, more than once.</p>
<p>The vowels in <code>s</code> are <code>['I', 'e', 'e', 'A']</code>. On reversing the vowels, s becomes <code>"AceCreIm"</code>.</p>