static isHeader_(data, offset) {
    /*
     * http://id3.org/id3v2.3.0
     * [0]     = 'I'
     * [1]     = 'D'
     * [2]     = '3'
     * [3,4]   = {Version}
     * [5]     = {Flags}
     * [6-9]   = {ID3 Size}
     *
     * An ID3v2 tag can be detected with the following pattern:
     *  $49 44 33 yy yy xx zz zz zz zz
     * Where yy is less than $FF, xx is the 'flags' byte and zz is less than $80
     */
    if (offset + 10 <= data.length) {
      // look for 'ID3' identifier
      if (data[offset] === 0x49 &&
          data[offset + 1] === 0x44 &&
          data[offset + 2] === 0x33) {
        // check version is within range
        if (data[offset + 3] < 0xff && data[offset + 4] < 0xff) {
          // check size is within range
          if (data[offset + 6] < 0x80 &&
              data[offset + 7] < 0x80 &&
              data[offset + 8] < 0x80 &&
              data[offset + 9] < 0x80) {
            return true;
          }
        }
      }
    }

    return false;
  }
@param {Uint8Array} data
@param {number} offset
@return {boolean}
@private