code: function __append_utf8(codepoint) {
  
          var mask;
          var bytes;
  
          // 1 byte
          if (codepoint <= 0x7F) {
              mask = 0x00;
              bytes = 1;
          }
  
          // 2 byte
          else if (codepoint <= 0x7FF) {
              mask = 0xC0;
              bytes = 2;
          }
  
          // 3 byte
          else if (codepoint <= 0xFFFF) {
              mask = 0xE0;
              bytes = 3;
          }
  
          // 4 byte
          else if (codepoint <= 0x1FFFFF) {
              mask = 0xF0;
              bytes = 4;
          }
  
          // If invalid codepoint, append replacement character
          else {
              __append_utf8(0xFFFD);
              return;
          }
  
          // Offset buffer by size
          __expand(bytes);
          var offset = length - 1;
  
          // Add trailing bytes, if any
          for (var i=1; i<bytes; i++) {
              buffer[offset--] = 0x80 | (codepoint & 0x3F);
              codepoint >>= 6;
          }
  
          // Set initial byte
          buffer[offset] = mask | codepoint;
  
      }
docs: Appends a single Unicode character to the current buffer, resizing the
  buffer if necessary. The character will be encoded as UTF-8.
  
  @private
  @param {Number} codepoint The codepoint of the Unicode character to
  append.