code: function(features) {
              if (!(features instanceof Array)) {
                  features = [features];
              }
              var result = this.toTriangles().map(function(triPoly) {
                      return triPoly.getTetraFeatures(features);
                  })
                  .reduce(function(pv, v) {
                      return v.map(function(feat, i) {
                          return feat + (pv === 0 ? 0 : pv[i]);
                      });
                  }, 0);
              return (result.length == 1) ? result[0] : result;
          }
docs: features: string, or array containing 1 or more strings of: 'volume', 'area' more could be added here (Fourier coeff, moments)