code: function (numeral, quality) {
    // Roman numeral representing chord
    this.numeral = numeral;
  
    // Chord quality: M, m, x, o, ø, s
    this.quality = quality;
    if (!_.contains(['M', 'm', 'x', 'o', 'ø', 's'], quality)) {
      throw new Error('Invalid chord quality');
    }
  
    // The number of half-steps between the key and the chord
    // e.g. I => 0, bIV => 6
    this.interval = getHalfSteps(numeral);
  
    this.toString = function () {
      return this.numeral + this.quality;
    };
  }
docs: A roman numeral symbol representing a chord using the Mehegan system