function onStartCubicMorph(tweenProp) {
    if (!KEC[tweenProp] && this.valuesEnd[tweenProp]) {
      KEC[tweenProp] = function updateMorph(elem, a, b, v) {
        var curve = [];
        var path1 = a.curve;
        var path2 = b.curve;
        for (var i = 0, l = path2.length; i < l; i += 1) { // each path command
          curve.push([path1[i][0]]);
          for (var j = 1, l2 = path1[i].length; j < l2; j += 1) { // each command coordinate
            /* eslint-disable-next-line no-bitwise -- impossible to satisfy */
            curve[i].push((numbers(path1[i][j], path2[i][j], v) * 1000 >> 0) / 1000);
          }
        }
        elem.setAttribute('d', v === 1 ? b.original : pathToString(curve));
      };
    }
  }
Sets the property update function.
@param {string} tweenProp the `path` property