code: function compareMessagesByFixRange(a, b) {
      return a.fix.range[0] - b.fix.range[0] || a.fix.range[1] - b.fix.range[1];
  }
docs: Compares items in a messages array by range.
  @param {Message} a The first message.
  @param {Message} b The second message.
  @returns {int} -1 if a comes before b, 1 if a comes after b, 0 if equal.
  @private