docs: function getEasing(value, duration) {
          var easing = value;
  
          /* The easing option can either be a string that references a pre-registered easing,
             or it can be a two-/four-item array of integers to be converted into a bezier/spring function. */
          if (Type.isString(value)) {
              /* Ensure that the easing has been assigned to jQuery's Velocity.Easings object. */
              if (!Velocity.Easings[value]) {
                  easing = false;
              }
          } else if (Type.isArray(value) && value.length === 1) {
              easing = generateStep.apply(null, value);
          } else if (Type.isArray(value) && value.length === 2) {
              /* springRK4 must be passed the animation's duration. */
              /* Note: If the springRK4 array contains non-numbers, generateSpringRK4() returns an easing
                 function generated with default tension and friction values. */
              easing = generateSpringRK4.apply(null, value.concat([ duration ]));
          } else if (Type.isArray(value) && value.length === 4) {
              /* Note: If the bezier array contains non-numbers, generateBezier() returns false. */
              easing = generateBezier.apply(null, value);
          } else {
              easing = false;
          }
  
          /* Revert to the Velocity-wide default easing type, or fall back to "swing" (which is also jQuery's default)
             if the Velocity-wide default has been incorrectly modified. */
          if (easing === false) {
              if (Velocity.Easings[Velocity.defaults.easing]) {
                  easing = Velocity.defaults.easing;
              } else {
                  easing = EASING_DEFAULT;
              }
          }
  
          return easing;
      }