docs: function (alteration) {
          var valid = /(?:n|b|\#|\+|\-)(?:\d+)/;
          if (!valid.test(alteration)) {
              return false;
          }
          var operation = alteration.slice(0, 1);
          var degree = alteration.slice(1);
          if (operation === '+') {
              operation = '#';
          }
          if (operation === '-') {
              operation = 'b';
          }
          if (operation === '#') {
              return 'A' + degree;
          }
          if (operation === 'b') {
              if (degree === '5' || degree === '11' || degree === '4') {
                  return 'd' + degree;
              }
              else {
                  return 'm' + degree;
              }
          }
          if (operation === 'n') {
              if (degree === '5' || degree === '11' || degree === '4') {
                  return 'P' + degree;
              }
              else {
                  return 'M' + degree;
              }
          }
      }