 var alphabet = _Base64Encoder._base64Alphabet;
  var inverseAlphabet = _Base64Decoder._inverseAlphabet;
  var firstPadding = -1;
  var firstPaddingSourceIndex = -1;
  var paddingCount = 0;
  for (var i = start; i &lt; end;) {
    var sliceEnd = i;
    var char = source.codeUnitAt(i++);
    var originalChar = char;
    &#47;&#47; Normalize char, keep originalChar to see if it matches the source.
    if (char == percent) {
      if (i + 2 &lt;= end) {
        char = parseHexByte(source, i); &#47;&#47; May be