toString() {
    var cfiString = "epubcfi(";
    cfiString += this.segmentString(this.base);
    cfiString += "!";
    cfiString += this.segmentString(this.path); // Add Range, if present

    if (this.range && this.start) {
      cfiString += ",";
      cfiString += this.segmentString(this.start);
    }

    if (this.range && this.end) {
      cfiString += ",";
      cfiString += this.segmentString(this.end);
    }

    cfiString += ")";
    return cfiString;
  }
Convert CFI to a epubcfi(...) string
@returns {string} epubcfi