docs: function() {
  
          /******************
              Call Chain
          ******************/
  
          /* Logic for determining what to return to the call stack when exiting out of Velocity. */
          function getChain () {
              /* If we are using the utility function, attempt to return this call's promise. If no promise library was detected,
                 default to null instead of returning the targeted elements so that utility function's return value is standardized. */
              if (isUtility) {
                  return promiseData.promise || null;
              /* Otherwise, if we're using $.fn, return the jQuery-/Zepto-wrapped element set. */
              } else {
                  return elementsWrapped;
              }
          }
  
          /*************************
             Arguments Assignment
          *************************/
  
          /* To allow for expressive CoffeeScript code, Velocity supports an alternative syntax in which "elements" (or "e"), "properties" (or "p"), and "options" (or "o")
             objects are defined on a container object that's passed in as Velocity's sole argument. */
          /* Note: Some browsers automatically populate arguments with a "properties" object. We detect it by checking for its default "names" property. */
          var syntacticSugar = (arguments[0] && (arguments[0].p || (($.isPlainObject(arguments[0].properties) && !arguments[0].properties.names) || Type.isString(arguments[0].properties)))),
              /* Whether Velocity was called via the utility function (as opposed to on a jQuery/Zepto object). */
              isUtility,
              /* When Velocity is called via the utility function ($.Velocity()/Velocity()), elements are explicitly
                 passed in as the first parameter. Thus, argument positioning varies. We normalize them here. */
              elementsWrapped,
              argumentIndex;
  
          var elements,
              propertiesMap,
              options;
  
          /* Detect jQuery/Zepto elements being animated via the $.fn method. */
          if (Type.isWrapped(this)) {
              isUtility = false;
  
              argumentIndex = 0;
              elements = this;
              elementsWrapped = this;
          /* Otherwise, raw elements are being animated via the utility function. */
          } else {
              isUtility = true;
  
              argumentIndex = 1;
              elements = syntacticSugar ? (arguments[0].elements || arguments[0].e) : arguments[0];
          }
  
          elements = sanitizeElements(elements);
  
          if (!elements) {
              return;
          }
  
          if (syntacticSugar) {
              propertiesMap = arguments[0].properties || arguments[0].p;
              options = arguments[0].options || arguments[0].o;
          } else {
              propertiesMap = arguments[argumentIndex];
              options = arguments[argumentIndex + 1];
          }
  
          /* The length of the element set (in the form of a nodeList or an array of elements) is defaulted to 1 in case a
             single raw DOM element is passed in (which doesn't contain a length property). */
          var elementsLength = elements.length,
              elementsIndex = 0;
  
          /***************************
              Argument Overloading
          ***************************/
  
          /* Support is included for jQuery's argument overloading: $.animate(propertyMap [, duration] [, easing] [, complete]).
             Overloading is detected by checking for the absence of an object being passed into options. */
          /* Note: The stop and finish actions do not accept animation options, and are therefore excluded from this check. */
          if (!/^(stop|finish)$/i.test(propertiesMap) && !$.isPlainObject(options)) {
              /* The utility function shifts all arguments one position to the right, so we adjust for that offset. */
              var startingArgumentPosition = argumentIndex + 1;
  
              options = {};
  
              /* Iterate through all options arguments */
              for (var i = startingArgumentPosition; i < arguments.length; i++) {
                  /* Treat a number as a duration. Parse it out. */
                  /* Note: The following RegEx will return true if passed an array with a number as its first item.
                     Thus, arrays are skipped from this check. */
                  if (!Type.isArray(arguments[i]) && (/^(fast|normal|slow)$/i.test(arguments[i]) || /^\d/.test(arguments[i]))) {
                      options.duration = arguments[i];
                  /* Treat strings and arrays as easings. */
                  } else if (Type.isString(arguments[i]) || Type.isArray(arguments[i])) {
                      options.easing = arguments[i];
                  /* Treat a function as a complete callback. */
                  } else if (Type.isFunction(arguments[i])) {
                      options.complete = arguments[i];
                  }
              }
          }
  
          /***************
              Promises
          ***************/
  
          var promiseData = {
                  promise: null,
                  resolver: null,
                  rejecter: null
              };
  
          /* If this call was made via the utility function (which is the default method of invocation when jQuery/Zepto are not being used), and if
             promise support was detected, create a promise object for this call and store references to its resolver and rejecter methods. The resolve
             method is used when a call completes naturally or is prematurely stopped by the user. In both cases, completeCall() handles the associated
             call cleanup and promise resolving logic. The reject method is used when an invalid set of arguments is passed into a Velocity call. */
          /* Note: Velocity employs a call-based queueing architecture, which means that stopping an animating element actually stops the full call that
             triggered it -- not that one element exclusively. Similarly, there is one promise per call, and all elements targeted by a Velocity call are
             grouped together for the purposes of resolving and rejecting a promise. */
          if (isUtility && Velocity.Promise) {
              promiseData.promise = new Velocity.Promise(function (resolve, reject) {
                  promiseData.resolver = resolve;
                  promiseData.rejecter = reject;
              });
          }
  
          /*********************
             Action Detection
          *********************/
  
          /* Velocity's behavior is categorized into "actions": Elements can either be specially scrolled into view,
             or they can be started, stopped, or reversed. If a literal or referenced properties map is passed in as Velocity's
             first argument, the associated action is "start". Alternatively, "scroll", "reverse", or "stop" can be passed in instead of a properties map. */
          var action;
  
          switch (propertiesMap) {
              case "scroll":
                  action = "scroll";
                  break;
  
              case "reverse":
                  action = "reverse";
                  break;
  
              case "finish":
              case "stop":
                  /*******************
                      Action: Stop
                  *******************/
  
                  /* Clear the currently-active delay on each targeted element. */
                  $.each(elements, function(i, element) {
                      if (Data(element) && Data(element).delayTimer) {
                          /* Stop the timer from triggering its cached next() function. */
                          clearTimeout(Data(element).delayTimer.setTimeout);
  
                          /* Manually call the next() function so that the subsequent queue items can progress. */
                          if (Data(element).delayTimer.next) {
                              Data(element).delayTimer.next();
                          }
  
                          delete Data(element).delayTimer;
                      }
                  });
  
                  var callsToStop = [];
  
                  /* When the stop action is triggered, the elements' currently active call is immediately stopped. The active call might have
                     been applied to multiple elements, in which case all of the call's elements will be stopped. When an element
                     is stopped, the next item in its animation queue is immediately triggered. */
                  /* An additional argument may be passed in to clear an element's remaining queued calls. Either true (which defaults to the "fx" queue)
                     or a custom queue string can be passed in. */
                  /* Note: The stop command runs prior to Velocity's Queueing phase since its behavior is intended to take effect *immediately*,
                     regardless of the element's current queue state. */
  
                  /* Iterate through every active call. */
                  $.each(Velocity.State.calls, function(i, activeCall) {
                      /* Inactive calls are set to false by the logic inside completeCall(). Skip them. */
                      if (activeCall) {
                          /* Iterate through the active call's targeted elements. */
                          $.each(activeCall[1], function(k, activeElement) {
                              /* If true was passed in as a secondary argument, clear absolutely all calls on this element. Otherwise, only
                                 clear calls associated with the relevant queue. */
                              /* Call stopping logic works as follows:
                                 - options === true --> stop current default queue calls (and queue:false calls), including remaining queued ones.
                                 - options === undefined --> stop current queue:"" call and all queue:false calls.
                                 - options === false --> stop only queue:false calls.
                                 - options === "custom" --> stop current queue:"custom" call, including remaining queued ones (there is no functionality to only clear the currently-running queue:"custom" call). */
                              var queueName = (options === undefined) ? "" : options;
  
                              if (queueName !== true && (activeCall[2].queue !== queueName) && !(options === undefined && activeCall[2].queue === false)) {
                                  return true;
                              }
  
                              /* Iterate through the calls targeted by the stop command. */
                              $.each(elements, function(l, element) {                                
                                  /* Check that this call was applied to the target element. */
                                  if (element === activeElement) {
                                      /* Optionally clear the remaining queued calls. */
                                      if (options === true || Type.isString(options)) {
                                          /* Iterate through the items in the element's queue. */
                                          $.each($.queue(element, Type.isString(options) ? options : ""), function(_, item) {
                                              /* The queue array can contain an "inprogress" string, which we skip. */
                                              if (Type.isFunction(item)) {
                                                  /* Pass the item's callback a flag indicating that we want to abort from the queue call.
                                                     (Specifically, the queue will resolve the call's associated promise then abort.)  */
                                                  item(null, true);
                                              }
                                          });
  
                                          /* Clearing the $.queue() array is achieved by resetting it to []. */
                                          $.queue(element, Type.isString(options) ? options : "", []);
                                      }
  
                                      if (propertiesMap === "stop") {
                                          /* Since "reverse" uses cached start values (the previous call's endValues), these values must be
                                             changed to reflect the final value that the elements were actually tweened to. */
                                          /* Note: If only queue:false animations are currently running on an element, it won't have a tweensContainer
                                             object. Also, queue:false animations can't be reversed. */
                                          if (Data(element) && Data(element).tweensContainer && queueName !== false) {
                                              $.each(Data(element).tweensContainer, function(m, activeTween) {
                                                  activeTween.endValue = activeTween.currentValue;
                                              });
                                          }
  
                                          callsToStop.push(i);
                                      } else if (propertiesMap === "finish") {
                                          /* To get active tweens to finish immediately, we forcefully shorten their durations to 1ms so that
                                          they finish upon the next rAf tick then proceed with normal call completion logic. */
                                          activeCall[2].duration = 1;
                                      }
                                  }
                              });
                          });
                      }
                  });
  
                  /* Prematurely call completeCall() on each matched active call. Pass an additional flag for "stop" to indicate
                     that the complete callback and display:none setting should be skipped since we're completing prematurely. */
                  if (propertiesMap === "stop") {
                      $.each(callsToStop, function(i, j) {
                          completeCall(j, true);
                      });
  
                      if (promiseData.promise) {
                          /* Immediately resolve the promise associated with this stop call since stop runs synchronously. */
                          promiseData.resolver(elements);
                      }
                  }
  
                  /* Since we're stopping, and not proceeding with queueing, exit out of Velocity. */
                  return getChain();
  
              default:
                  /* Treat a non-empty plain object as a literal properties map. */
                  if ($.isPlainObject(propertiesMap) && !Type.isEmptyObject(propertiesMap)) {
                      action = "start";
  
                  /****************
                      Redirects
                  ****************/
  
                  /* Check if a string matches a registered redirect (see Redirects above). */
                  } else if (Type.isString(propertiesMap) && Velocity.Redirects[propertiesMap]) {
                      var opts = $.extend({}, options),
                          durationOriginal = opts.duration,
                          delayOriginal = opts.delay || 0;
  
                      /* If the backwards option was passed in, reverse the element set so that elements animate from the last to the first. */
                      if (opts.backwards === true) {
                          elements = $.extend(true, [], elements).reverse();
                      }
  
                      /* Individually trigger the redirect for each element in the set to prevent users from having to handle iteration logic in their redirect. */
                      $.each(elements, function(elementIndex, element) {
                          /* If the stagger option was passed in, successively delay each element by the stagger value (in ms). Retain the original delay value. */
                          if (parseFloat(opts.stagger)) {
                              opts.delay = delayOriginal + (parseFloat(opts.stagger) * elementIndex);
                          } else if (Type.isFunction(opts.stagger)) {
                              opts.delay = delayOriginal + opts.stagger.call(element, elementIndex, elementsLength);
                          }
  
                          /* If the drag option was passed in, successively increase/decrease (depending on the presense of opts.backwards)
                             the duration of each element's animation, using floors to prevent producing very short durations. */
                          if (opts.drag) {
                              /* Default the duration of UI pack effects (callouts and transitions) to 1000ms instead of the usual default duration of 400ms. */
                              opts.duration = parseFloat(durationOriginal) || (/^(callout|transition)/.test(propertiesMap) ? 1000 : DURATION_DEFAULT);
  
                              /* For each element, take the greater duration of: A) animation completion percentage relative to the original duration,
                                 B) 75% of the original duration, or C) a 200ms fallback (in case duration is already set to a low value).
                                 The end result is a baseline of 75% of the redirect's duration that increases/decreases as the end of the element set is approached. */
                              opts.duration = Math.max(opts.duration * (opts.backwards ? 1 - elementIndex/elementsLength : (elementIndex + 1) / elementsLength), opts.duration * 0.75, 200);
                          }
  
                          /* Pass in the call's opts object so that the redirect can optionally extend it. It defaults to an empty object instead of null to
                             reduce the opts checking logic required inside the redirect. */
                          Velocity.Redirects[propertiesMap].call(element, element, opts || {}, elementIndex, elementsLength, elements, promiseData.promise ? promiseData : undefined);
                      });
  
                      /* Since the animation logic resides within the redirect's own code, abort the remainder of this call.
                         (The performance overhead up to this point is virtually non-existant.) */
                      /* Note: The jQuery call chain is kept intact by returning the complete element set. */
                      return getChain();
                  } else {
                      var abortError = "Velocity: First argument (" + propertiesMap + ") was not a property map, a known action, or a registered redirect. Aborting.";
  
                      if (promiseData.promise) {
                          promiseData.rejecter(new Error(abortError));
                      } else {
                          console.log(abortError);
                      }
  
                      return getChain();
                  }
          }
  
          /**************************
              Call-Wide Variables
          **************************/
  
          /* A container for CSS unit conversion ratios (e.g. %, rem, and em ==> px) that is used to cache ratios across all elements
             being animated in a single Velocity call. Calculating unit ratios necessitates DOM querying and updating, and is therefore
             avoided (via caching) wherever possible. This container is call-wide instead of page-wide to avoid the risk of using stale
             conversion metrics across Velocity animations that are not immediately consecutively chained. */
          var callUnitConversionData = {
                  lastParent: null,
                  lastPosition: null,
                  lastFontSize: null,
                  lastPercentToPxWidth: null,
                  lastPercentToPxHeight: null,
                  lastEmToPx: null,
                  remToPx: null,
                  vwToPx: null,
                  vhToPx: null
              };
  
          /* A container for all the ensuing tween data and metadata associated with this call. This container gets pushed to the page-wide
             Velocity.State.calls array that is processed during animation ticking. */
          var call = [];
  
          /************************
             Element Processing
          ************************/
  
          /* Element processing consists of three parts -- data processing that cannot go stale and data processing that *can* go stale (i.e. third-party style modifications):
             1) Pre-Queueing: Element-wide variables, including the element's data storage, are instantiated. Call options are prepared. If triggered, the Stop action is executed.
             2) Queueing: The logic that runs once this call has reached its point of execution in the element's $.queue() stack. Most logic is placed here to avoid risking it becoming stale.
             3) Pushing: Consolidation of the tween data followed by its push onto the global in-progress calls container.
          */
  
          function processElement () {
  
              /*************************
                 Part I: Pre-Queueing
              *************************/
  
              /***************************
                 Element-Wide Variables
              ***************************/
  
              var element = this,
                  /* The runtime opts object is the extension of the current call's options and Velocity's page-wide option defaults. */
                  opts = $.extend({}, Velocity.defaults, options),
                  /* A container for the processed data associated with each property in the propertyMap.
                     (Each property in the map produces its own "tween".) */
                  tweensContainer = {},
                  elementUnitConversionData;
  
              /******************
                 Element Init
              ******************/
  
              if (Data(element) === undefined) {
                  Velocity.init(element);
              }
  
              /******************
                 Option: Delay
              ******************/
  
              /* Since queue:false doesn't respect the item's existing queue, we avoid injecting its delay here (it's set later on). */
              /* Note: Velocity rolls its own delay function since jQuery doesn't have a utility alias for $.fn.delay()
                 (and thus requires jQuery element creation, which we avoid since its overhead includes DOM querying). */
              if (parseFloat(opts.delay) && opts.queue !== false) {
                  $.queue(element, opts.queue, function(next) {
                      /* This is a flag used to indicate to the upcoming completeCall() function that this queue entry was initiated by Velocity. See completeCall() for further details. */
                      Velocity.velocityQueueEntryFlag = true;
  
                      /* The ensuing queue item (which is assigned to the "next" argument that $.queue() automatically passes in) will be triggered after a setTimeout delay.
                         The setTimeout is stored so that it can be subjected to clearTimeout() if this animation is prematurely stopped via Velocity's "stop" command. */
                      Data(element).delayTimer = {
                          setTimeout: setTimeout(next, parseFloat(opts.delay)),
                          next: next
                      };
                  });
              }
  
              /*********************
                 Option: Duration
              *********************/
  
              /* Support for jQuery's named durations. */
              switch (opts.duration.toString().toLowerCase()) {
                  case "fast":
                      opts.duration = 200;
                      break;
  
                  case "normal":
                      opts.duration = DURATION_DEFAULT;
                      break;
  
                  case "slow":
                      opts.duration = 600;
                      break;
  
                  default:
                      /* Remove the potential "ms" suffix and default to 1 if the user is attempting to set a duration of 0 (in order to produce an immediate style change). */
                      opts.duration = parseFloat(opts.duration) || 1;
              }
  
              /************************
                 Global Option: Mock
              ************************/
  
              if (Velocity.mock !== false) {
                  /* In mock mode, all animations are forced to 1ms so that they occur immediately upon the next rAF tick.
                     Alternatively, a multiplier can be passed in to time remap all delays and durations. */
                  if (Velocity.mock === true) {
                      opts.duration = opts.delay = 1;
                  } else {
                      opts.duration *= parseFloat(Velocity.mock) || 1;
                      opts.delay *= parseFloat(Velocity.mock) || 1;
                  }
              }
  
              /*******************
                 Option: Easing
              *******************/
  
              opts.easing = getEasing(opts.easing, opts.duration);
  
              /**********************
                 Option: Callbacks
              **********************/
  
              /* Callbacks must functions. Otherwise, default to null. */
              if (opts.begin && !Type.isFunction(opts.begin)) {
                  opts.begin = null;
              }
  
              if (opts.progress && !Type.isFunction(opts.progress)) {
                  opts.progress = null;
              }
  
              if (opts.complete && !Type.isFunction(opts.complete)) {
                  opts.complete = null;
              }
  
              /*********************************
                 Option: Display & Visibility
              *********************************/
  
              /* Refer to Velocity's documentation (VelocityJS.org/#displayAndVisibility) for a description of the display and visibility options' behavior. */
              /* Note: We strictly check for undefined instead of falsiness because display accepts an empty string value. */
              if (opts.display !== undefined && opts.display !== null) {
                  opts.display = opts.display.toString().toLowerCase();
  
                  /* Users can pass in a special "auto" value to instruct Velocity to set the element to its default display value. */
                  if (opts.display === "auto") {
                      opts.display = Velocity.CSS.Values.getDisplayType(element);
                  }
              }
  
              if (opts.visibility !== undefined && opts.visibility !== null) {
                  opts.visibility = opts.visibility.toString().toLowerCase();
              }
  
              /**********************
                 Option: mobileHA
              **********************/
  
              /* When set to true, and if this is a mobile device, mobileHA automatically enables hardware acceleration (via a null transform hack)
                 on animating elements. HA is removed from the element at the completion of its animation. */
              /* Note: Android Gingerbread doesn't support HA. If a null transform hack (mobileHA) is in fact set, it will prevent other tranform subproperties from taking effect. */
              /* Note: You can read more about the use of mobileHA in Velocity's documentation: VelocityJS.org/#mobileHA. */
              opts.mobileHA = (opts.mobileHA && Velocity.State.isMobile && !Velocity.State.isGingerbread);
  
              /***********************
                 Part II: Queueing
              ***********************/
  
              /* When a set of elements is targeted by a Velocity call, the set is broken up and each element has the current Velocity call individually queued onto it.
                 In this way, each element's existing queue is respected; some elements may already be animating and accordingly should not have this current Velocity call triggered immediately. */
              /* In each queue, tween data is processed for each animating property then pushed onto the call-wide calls array. When the last element in the set has had its tweens processed,
                 the call array is pushed to Velocity.State.calls for live processing by the requestAnimationFrame tick. */
              function buildQueue (next) {
  
                  /*******************
                     Option: Begin
                  *******************/
  
                  /* The begin callback is fired once per call -- not once per elemenet -- and is passed the full raw DOM element set as both its context and its first argument. */
                  if (opts.begin && elementsIndex === 0) {
                      /* We throw callbacks in a setTimeout so that thrown errors don't halt the execution of Velocity itself. */
                      try {
                          opts.begin.call(elements, elements);
                      } catch (error) {
                          setTimeout(function() { throw error; }, 1);
                      }
                  }
  
                  /*****************************************
                     Tween Data Construction (for Scroll)
                  *****************************************/
  
                  /* Note: In order to be subjected to chaining and animation options, scroll's tweening is routed through Velocity as if it were a standard CSS property animation. */
                  if (action === "scroll") {
                      /* The scroll action uniquely takes an optional "offset" option -- specified in pixels -- that offsets the targeted scroll position. */
                      var scrollDirection = (/^x$/i.test(opts.axis) ? "Left" : "Top"),
                          scrollOffset = parseFloat(opts.offset) || 0,
                          scrollPositionCurrent,
                          scrollPositionCurrentAlternate,
                          scrollPositionEnd;
  
                      /* Scroll also uniquely takes an optional "container" option, which indicates the parent element that should be scrolled --
                         as opposed to the browser window itself. This is useful for scrolling toward an element that's inside an overflowing parent element. */
                      if (opts.container) {
                          /* Ensure that either a jQuery object or a raw DOM element was passed in. */
                          if (Type.isWrapped(opts.container) || Type.isNode(opts.container)) {
                              /* Extract the raw DOM element from the jQuery wrapper. */
                              opts.container = opts.container[0] || opts.container;
                              /* Note: Unlike other properties in Velocity, the browser's scroll position is never cached since it so frequently changes
                                 (due to the user's natural interaction with the page). */
                              scrollPositionCurrent = opts.container["scroll" + scrollDirection]; /* GET */
  
                              /* $.position() values are relative to the container's currently viewable area (without taking into account the container's true dimensions
                                 -- say, for example, if the container was not overflowing). Thus, the scroll end value is the sum of the child element's position *and*
                                 the scroll container's current scroll position. */
                              scrollPositionEnd = (scrollPositionCurrent + $(element).position()[scrollDirection.toLowerCase()]) + scrollOffset; /* GET */
                          /* If a value other than a jQuery object or a raw DOM element was passed in, default to null so that this option is ignored. */
                          } else {
                              opts.container = null;
                          }
                      } else {
                          /* If the window itself is being scrolled -- not a containing element -- perform a live scroll position lookup using
                             the appropriate cached property names (which differ based on browser type). */
                          scrollPositionCurrent = Velocity.State.scrollAnchor[Velocity.State["scrollProperty" + scrollDirection]]; /* GET */
                          /* When scrolling the browser window, cache the alternate axis's current value since window.scrollTo() doesn't let us change only one value at a time. */
                          scrollPositionCurrentAlternate = Velocity.State.scrollAnchor[Velocity.State["scrollProperty" + (scrollDirection === "Left" ? "Top" : "Left")]]; /* GET */
  
                          /* Unlike $.position(), $.offset() values are relative to the browser window's true dimensions -- not merely its currently viewable area --
                             and therefore end values do not need to be compounded onto current values. */
                          scrollPositionEnd = $(element).offset()[scrollDirection.toLowerCase()] + scrollOffset; /* GET */
                      }
  
                      /* Since there's only one format that scroll's associated tweensContainer can take, we create it manually. */
                      tweensContainer = {
                          scroll: {
                              rootPropertyValue: false,
                              startValue: scrollPositionCurrent,
                              currentValue: scrollPositionCurrent,
                              endValue: scrollPositionEnd,
                              unitType: "",
                              easing: opts.easing,
                              scrollData: {
                                  container: opts.container,
                                  direction: scrollDirection,
                                  alternateValue: scrollPositionCurrentAlternate
                              }
                          },
                          element: element
                      };
  
                      if (Velocity.debug) console.log("tweensContainer (scroll): ", tweensContainer.scroll, element);
  
                  /******************************************
                     Tween Data Construction (for Reverse)
                  ******************************************/
  
                  /* Reverse acts like a "start" action in that a property map is animated toward. The only difference is
                     that the property map used for reverse is the inverse of the map used in the previous call. Thus, we manipulate
                     the previous call to construct our new map: use the previous map's end values as our new map's start values. Copy over all other data. */
                  /* Note: Reverse can be directly called via the "reverse" parameter, or it can be indirectly triggered via the loop option. (Loops are composed of multiple reverses.) */
                  /* Note: Reverse calls do not need to be consecutively chained onto a currently-animating element in order to operate on cached values;
                     there is no harm to reverse being called on a potentially stale data cache since reverse's behavior is simply defined
                     as reverting to the element's values as they were prior to the previous *Velocity* call. */
                  } else if (action === "reverse") {
                      /* Abort if there is no prior animation data to reverse to. */
                      if (!Data(element).tweensContainer) {
                          /* Dequeue the element so that this queue entry releases itself immediately, allowing subsequent queue entries to run. */
                          $.dequeue(element, opts.queue);
  
                          return;
                      } else {
                          /*********************
                             Options Parsing
                          *********************/
  
                          /* If the element was hidden via the display option in the previous call,
                             revert display to "auto" prior to reversal so that the element is visible again. */
                          if (Data(element).opts.display === "none") {
                              Data(element).opts.display = "auto";
                          }
  
                          if (Data(element).opts.visibility === "hidden") {
                              Data(element).opts.visibility = "visible";
                          }
  
                          /* If the loop option was set in the previous call, disable it so that "reverse" calls aren't recursively generated.
                             Further, remove the previous call's callback options; typically, users do not want these to be refired. */
                          Data(element).opts.loop = false;
                          Data(element).opts.begin = null;
                          Data(element).opts.complete = null;
  
                          /* Since we're extending an opts object that has already been extended with the defaults options object,
                             we remove non-explicitly-defined properties that are auto-assigned values. */
                          if (!options.easing) {
                              delete opts.easing;
                          }
  
                          if (!options.duration) {
                              delete opts.duration;
                          }
  
                          /* The opts object used for reversal is an extension of the options object optionally passed into this
                             reverse call plus the options used in the previous Velocity call. */
                          opts = $.extend({}, Data(element).opts, opts);
  
                          /*************************************
                             Tweens Container Reconstruction
                          *************************************/
  
                          /* Create a deepy copy (indicated via the true flag) of the previous call's tweensContainer. */
                          var lastTweensContainer = $.extend(true, {}, Data(element).tweensContainer);
  
                          /* Manipulate the previous tweensContainer by replacing its end values and currentValues with its start values. */
                          for (var lastTween in lastTweensContainer) {
                              /* In addition to tween data, tweensContainers contain an element property that we ignore here. */
                              if (lastTween !== "element") {
                                  var lastStartValue = lastTweensContainer[lastTween].startValue;
  
                                  lastTweensContainer[lastTween].startValue = lastTweensContainer[lastTween].currentValue = lastTweensContainer[lastTween].endValue;
                                  lastTweensContainer[lastTween].endValue = lastStartValue;
  
                                  /* Easing is the only option that embeds into the individual tween data (since it can be defined on a per-property basis).
                                     Accordingly, every property's easing value must be updated when an options object is passed in with a reverse call.
                                     The side effect of this extensibility is that all per-property easing values are forcefully reset to the new value. */
                                  if (!Type.isEmptyObject(options)) {
                                      lastTweensContainer[lastTween].easing = opts.easing;
                                  }
  
                                  if (Velocity.debug) console.log("reverse tweensContainer (" + lastTween + "): " + JSON.stringify(lastTweensContainer[lastTween]), element);
                              }
                          }
  
                          tweensContainer = lastTweensContainer;
                      }
  
                  /*****************************************
                     Tween Data Construction (for Start)
                  *****************************************/
  
                  } else if (action === "start") {
  
                      /*************************
                          Value Transferring
                      *************************/
  
                      /* If this queue entry follows a previous Velocity-initiated queue entry *and* if this entry was created
                         while the element was in the process of being animated by Velocity, then this current call is safe to use
                         the end values from the prior call as its start values. Velocity attempts to perform this value transfer
                         process whenever possible in order to avoid requerying the DOM. */
                      /* If values aren't transferred from a prior call and start values were not forcefed by the user (more on this below),
                         then the DOM is queried for the element's current values as a last resort. */
                      /* Note: Conversely, animation reversal (and looping) *always* perform inter-call value transfers; they never requery the DOM. */
                      var lastTweensContainer;
  
                      /* The per-element isAnimating flag is used to indicate whether it's safe (i.e. the data isn't stale)
                         to transfer over end values to use as start values. If it's set to true and there is a previous
                         Velocity call to pull values from, do so. */
                      if (Data(element).tweensContainer && Data(element).isAnimating === true) {
                          lastTweensContainer = Data(element).tweensContainer;
                      }
  
                      /***************************
                         Tween Data Calculation
                      ***************************/
  
                      /* This function parses property data and defaults endValue, easing, and startValue as appropriate. */
                      /* Property map values can either take the form of 1) a single value representing the end value,
                         or 2) an array in the form of [ endValue, [, easing] [, startValue] ].
                         The optional third parameter is a forcefed startValue to be used instead of querying the DOM for
                         the element's current value. Read Velocity's docmentation to learn more about forcefeeding: VelocityJS.org/#forcefeeding */
                      function parsePropertyValue (valueData, skipResolvingEasing) {
                          var endValue = undefined,
                              easing = undefined,
                              startValue = undefined;
  
                          /* Handle the array format, which can be structured as one of three potential overloads:
                             A) [ endValue, easing, startValue ], B) [ endValue, easing ], or C) [ endValue, startValue ] */
                          if (Type.isArray(valueData)) {
                              /* endValue is always the first item in the array. Don't bother validating endValue's value now
                                 since the ensuing property cycling logic does that. */
                              endValue = valueData[0];
  
                              /* Two-item array format: If the second item is a number, function, or hex string, treat it as a
                                 start value since easings can only be non-hex strings or arrays. */
                              if ((!Type.isArray(valueData[1]) && /^[\d-]/.test(valueData[1])) || Type.isFunction(valueData[1]) || CSS.RegEx.isHex.test(valueData[1])) {
                                  startValue = valueData[1];
                              /* Two or three-item array: If the second item is a non-hex string or an array, treat it as an easing. */
                              } else if ((Type.isString(valueData[1]) && !CSS.RegEx.isHex.test(valueData[1])) || Type.isArray(valueData[1])) {
                                  easing = skipResolvingEasing ? valueData[1] : getEasing(valueData[1], opts.duration);
  
                                  /* Don't bother validating startValue's value now since the ensuing property cycling logic inherently does that. */
                                  if (valueData[2] !== undefined) {
                                      startValue = valueData[2];
                                  }
                              }
                          /* Handle the single-value format. */
                          } else {
                              endValue = valueData;
                          }
  
                          /* Default to the call's easing if a per-property easing type was not defined. */
                          if (!skipResolvingEasing) {
                              easing = easing || opts.easing;
                          }
  
                          /* If functions were passed in as values, pass the function the current element as its context,
                             plus the element's index and the element set's size as arguments. Then, assign the returned value. */
                          if (Type.isFunction(endValue)) {
                              endValue = endValue.call(element, elementsIndex, elementsLength);
                          }
  
                          if (Type.isFunction(startValue)) {
                              startValue = startValue.call(element, elementsIndex, elementsLength);
                          }
  
                          /* Allow startValue to be left as undefined to indicate to the ensuing code that its value was not forcefed. */
                          return [ endValue || 0, easing, startValue ];
                      }
  
                      /* Cycle through each property in the map, looking for shorthand color properties (e.g. "color" as opposed to "colorRed"). Inject the corresponding
                         colorRed, colorGreen, and colorBlue RGB component tweens into the propertiesMap (which Velocity understands) and remove the shorthand property. */
                      $.each(propertiesMap, function(property, value) {
                          /* Find shorthand color properties that have been passed a hex string. */
                          if (RegExp("^" + CSS.Lists.colors.join("$|^") + "$").test(property)) {
                              /* Parse the value data for each shorthand. */
                              var valueData = parsePropertyValue(value, true),
                                  endValue = valueData[0],
                                  easing = valueData[1],
                                  startValue = valueData[2];
  
                              if (CSS.RegEx.isHex.test(endValue)) {
                                  /* Convert the hex strings into their RGB component arrays. */
                                  var colorComponents = [ "Red", "Green", "Blue" ],
                                      endValueRGB = CSS.Values.hexToRgb(endValue),
                                      startValueRGB = startValue ? CSS.Values.hexToRgb(startValue) : undefined;
  
                                  /* Inject the RGB component tweens into propertiesMap. */
                                  for (var i = 0; i < colorComponents.length; i++) {
                                      var dataArray = [ endValueRGB[i] ];
  
                                      if (easing) {
                                          dataArray.push(easing);
                                      }
  
                                      if (startValueRGB !== undefined) {
                                          dataArray.push(startValueRGB[i]);
                                      }
  
                                      propertiesMap[property + colorComponents[i]] = dataArray;
                                  }
  
                                  /* Remove the intermediary shorthand property entry now that we've processed it. */
                                  delete propertiesMap[property];
                              }
                          }
                      });
  
                      /* Create a tween out of each property, and append its associated data to tweensContainer. */
                      for (var property in propertiesMap) {
  
                          /**************************
                             Start Value Sourcing
                          **************************/
  
                          /* Parse out endValue, easing, and startValue from the property's data. */
                          var valueData = parsePropertyValue(propertiesMap[property]),
                              endValue = valueData[0],
                              easing = valueData[1],
                              startValue = valueData[2];
  
                          /* Now that the original property name's format has been used for the parsePropertyValue() lookup above,
                             we force the property to its camelCase styling to normalize it for manipulation. */
                          property = CSS.Names.camelCase(property);
  
                          /* In case this property is a hook, there are circumstances where we will intend to work on the hook's root property and not the hooked subproperty. */
                          var rootProperty = CSS.Hooks.getRoot(property),
                              rootPropertyValue = false;
  
                          /* Other than for the dummy tween property, properties that are not supported by the browser (and do not have an associated normalization) will
                             inherently produce no style changes when set, so they are skipped in order to decrease animation tick overhead.
                             Property support is determined via prefixCheck(), which returns a false flag when no supported is detected. */
                          /* Note: Since SVG elements have some of their properties directly applied as HTML attributes,
                             there is no way to check for their explicit browser support, and so we skip skip this check for them. */
                          if (!Data(element).isSVG && rootProperty !== "tween" && CSS.Names.prefixCheck(rootProperty)[1] === false && CSS.Normalizations.registered[rootProperty] === undefined) {
                              if (Velocity.debug) console.log("Skipping [" + rootProperty + "] due to a lack of browser support.");
  
                              continue;
                          }
  
                          /* If the display option is being set to a non-"none" (e.g. "block") and opacity (filter on IE<=8) is being
                             animated to an endValue of non-zero, the user's intention is to fade in from invisible, thus we forcefeed opacity
                             a startValue of 0 if its startValue hasn't already been sourced by value transferring or prior forcefeeding. */
                          if (((opts.display !== undefined && opts.display !== null && opts.display !== "none") || (opts.visibility !== undefined && opts.visibility !== "hidden")) && /opacity|filter/.test(property) && !startValue && endValue !== 0) {
                              startValue = 0;
                          }
  
                          /* If values have been transferred from the previous Velocity call, extract the endValue and rootPropertyValue
                             for all of the current call's properties that were *also* animated in the previous call. */
                          /* Note: Value transferring can optionally be disabled by the user via the _cacheValues option. */
                          if (opts._cacheValues && lastTweensContainer && lastTweensContainer[property]) {
                              if (startValue === undefined) {
                                  startValue = lastTweensContainer[property].endValue + lastTweensContainer[property].unitType;
                              }
  
                              /* The previous call's rootPropertyValue is extracted from the element's data cache since that's the
                                 instance of rootPropertyValue that gets freshly updated by the tweening process, whereas the rootPropertyValue
                                 attached to the incoming lastTweensContainer is equal to the root property's value prior to any tweening. */
                              rootPropertyValue = Data(element).rootPropertyValueCache[rootProperty];
                          /* If values were not transferred from a previous Velocity call, query the DOM as needed. */
                          } else {
                              /* Handle hooked properties. */
                              if (CSS.Hooks.registered[property]) {
                                 if (startValue === undefined) {
                                      rootPropertyValue = CSS.getPropertyValue(element, rootProperty); /* GET */
                                      /* Note: The following getPropertyValue() call does not actually trigger a DOM query;
                                         getPropertyValue() will extract the hook from rootPropertyValue. */
                                      startValue = CSS.getPropertyValue(element, property, rootPropertyValue);
                                  /* If startValue is already defined via forcefeeding, do not query the DOM for the root property's value;
                                     just grab rootProperty's zero-value template from CSS.Hooks. This overwrites the element's actual
                                     root property value (if one is set), but this is acceptable since the primary reason users forcefeed is
                                     to avoid DOM queries, and thus we likewise avoid querying the DOM for the root property's value. */
                                  } else {
                                      /* Grab this hook's zero-value template, e.g. "0px 0px 0px black". */
                                      rootPropertyValue = CSS.Hooks.templates[rootProperty][1];
                                  }
                              /* Handle non-hooked properties that haven't already been defined via forcefeeding. */
                              } else if (startValue === undefined) {
                                  startValue = CSS.getPropertyValue(element, property); /* GET */
                              }
                          }
  
                          /**************************
                             Value Data Extraction
                          **************************/
  
                          var separatedValue,
                              endValueUnitType,
                              startValueUnitType,
                              operator = false;
  
                          /* Separates a property value into its numeric value and its unit type. */
                          function separateValue (property, value) {
                              var unitType,
                                  numericValue;
  
                              numericValue = (value || "0")
                                  .toString()
                                  .toLowerCase()
                                  /* Match the unit type at the end of the value. */
                                  .replace(/[%A-z]+$/, function(match) {
                                      /* Grab the unit type. */
                                      unitType = match;
  
                                      /* Strip the unit type off of value. */
                                      return "";
                                  });
  
                              /* If no unit type was supplied, assign one that is appropriate for this property (e.g. "deg" for rotateZ or "px" for width). */
                              if (!unitType) {
                                  unitType = CSS.Values.getUnitType(property);
                              }
  
                              return [ numericValue, unitType ];
                          }
  
                          /* Separate startValue. */
                          separatedValue = separateValue(property, startValue);
                          startValue = separatedValue[0];
                          startValueUnitType = separatedValue[1];
  
                          /* Separate endValue, and extract a value operator (e.g. "+=", "-=") if one exists. */
                          separatedValue = separateValue(property, endValue);
                          endValue = separatedValue[0].replace(/^([+-\/*])=/, function(match, subMatch) {
                              operator = subMatch;
  
                              /* Strip the operator off of the value. */
                              return "";
                          });
                          endValueUnitType = separatedValue[1];
  
                          /* Parse float values from endValue and startValue. Default to 0 if NaN is returned. */
                          startValue = parseFloat(startValue) || 0;
                          endValue = parseFloat(endValue) || 0;
  
                          /***************************************
                             Property-Specific Value Conversion
                          ***************************************/
  
                          /* Custom support for properties that don't actually accept the % unit type, but where pollyfilling is trivial and relatively foolproof. */
                          if (endValueUnitType === "%") {
                              /* A %-value fontSize/lineHeight is relative to the parent's fontSize (as opposed to the parent's dimensions),
                                 which is identical to the em unit's behavior, so we piggyback off of that. */
                              if (/^(fontSize|lineHeight)$/.test(property)) {
                                  /* Convert % into an em decimal value. */
                                  endValue = endValue / 100;
                                  endValueUnitType = "em";
                              /* For scaleX and scaleY, convert the value into its decimal format and strip off the unit type. */
                              } else if (/^scale/.test(property)) {
                                  endValue = endValue / 100;
                                  endValueUnitType = "";
                              /* For RGB components, take the defined percentage of 255 and strip off the unit type. */
                              } else if (/(Red|Green|Blue)$/i.test(property)) {
                                  endValue = (endValue / 100) * 255;
                                  endValueUnitType = "";
                              }
                          }
  
                          /***************************
                             Unit Ratio Calculation
                          ***************************/
  
                          /* When queried, the browser returns (most) CSS property values in pixels. Therefore, if an endValue with a unit type of
                             %, em, or rem is animated toward, startValue must be converted from pixels into the same unit type as endValue in order
                             for value manipulation logic (increment/decrement) to proceed. Further, if the startValue was forcefed or transferred
                             from a previous call, startValue may also not be in pixels. Unit conversion logic therefore consists of two steps:
                             1) Calculating the ratio of %/em/rem/vh/vw relative to pixels
                             2) Converting startValue into the same unit of measurement as endValue based on these ratios. */
                          /* Unit conversion ratios are calculated by inserting a sibling node next to the target node, copying over its position property,
                             setting values with the target unit type then comparing the returned pixel value. */
                          /* Note: Even if only one of these unit types is being animated, all unit ratios are calculated at once since the overhead
                             of batching the SETs and GETs together upfront outweights the potential overhead
                             of layout thrashing caused by re-querying for uncalculated ratios for subsequently-processed properties. */
                          /* Todo: Shift this logic into the calls' first tick instance so that it's synced with RAF. */
                          function calculateUnitRatios () {
  
                              /************************
                                  Same Ratio Checks
                              ************************/
  
                              /* The properties below are used to determine whether the element differs sufficiently from this call's
                                 previously iterated element to also differ in its unit conversion ratios. If the properties match up with those
                                 of the prior element, the prior element's conversion ratios are used. Like most optimizations in Velocity,
                                 this is done to minimize DOM querying. */
                              var sameRatioIndicators = {
                                      myParent: element.parentNode || document.body, /* GET */
                                      position: CSS.getPropertyValue(element, "position"), /* GET */
                                      fontSize: CSS.getPropertyValue(element, "fontSize") /* GET */
                                  },
                                  /* Determine if the same % ratio can be used. % is based on the element's position value and its parent's width and height dimensions. */
                                  samePercentRatio = ((sameRatioIndicators.position === callUnitConversionData.lastPosition) && (sameRatioIndicators.myParent === callUnitConversionData.lastParent)),
                                  /* Determine if the same em ratio can be used. em is relative to the element's fontSize. */
                                  sameEmRatio = (sameRatioIndicators.fontSize === callUnitConversionData.lastFontSize);
  
                              /* Store these ratio indicators call-wide for the next element to compare against. */
                              callUnitConversionData.lastParent = sameRatioIndicators.myParent;
                              callUnitConversionData.lastPosition = sameRatioIndicators.position;
                              callUnitConversionData.lastFontSize = sameRatioIndicators.fontSize;
  
                              /***************************
                                 Element-Specific Units
                              ***************************/
  
                              /* Note: IE8 rounds to the nearest pixel when returning CSS values, thus we perform conversions using a measurement
                                 of 100 (instead of 1) to give our ratios a precision of at least 2 decimal values. */
                              var measurement = 100,
                                  unitRatios = {};
  
                              if (!sameEmRatio || !samePercentRatio) {
                                  var dummy = Data(element).isSVG ? document.createElementNS("http://www.w3.org/2000/svg", "rect") : document.createElement("div");
  
                                  Velocity.init(dummy);
                                  sameRatioIndicators.myParent.appendChild(dummy);
  
                                  /* To accurately and consistently calculate conversion ratios, the element's cascaded overflow and box-sizing are stripped.
                                     Similarly, since width/height can be artificially constrained by their min-/max- equivalents, these are controlled for as well. */
                                  /* Note: Overflow must be also be controlled for per-axis since the overflow property overwrites its per-axis values. */
                                  $.each([ "overflow", "overflowX", "overflowY" ], function(i, property) {
                                      Velocity.CSS.setPropertyValue(dummy, property, "hidden");
                                  });
                                  Velocity.CSS.setPropertyValue(dummy, "position", sameRatioIndicators.position);
                                  Velocity.CSS.setPropertyValue(dummy, "fontSize", sameRatioIndicators.fontSize);
                                  Velocity.CSS.setPropertyValue(dummy, "boxSizing", "content-box");
  
                                  /* width and height act as our proxy properties for measuring the horizontal and vertical % ratios. */
                                  $.each([ "minWidth", "maxWidth", "width", "minHeight", "maxHeight", "height" ], function(i, property) {
                                      Velocity.CSS.setPropertyValue(dummy, property, measurement + "%");
                                  });
                                  /* paddingLeft arbitrarily acts as our proxy property for the em ratio. */
                                  Velocity.CSS.setPropertyValue(dummy, "paddingLeft", measurement + "em");
  
                                  /* Divide the returned value by the measurement to get the ratio between 1% and 1px. Default to 1 since working with 0 can produce Infinite. */
                                  unitRatios.percentToPxWidth = callUnitConversionData.lastPercentToPxWidth = (parseFloat(CSS.getPropertyValue(dummy, "width", null, true)) || 1) / measurement; /* GET */
                                  unitRatios.percentToPxHeight = callUnitConversionData.lastPercentToPxHeight = (parseFloat(CSS.getPropertyValue(dummy, "height", null, true)) || 1) / measurement; /* GET */
                                  unitRatios.emToPx = callUnitConversionData.lastEmToPx = (parseFloat(CSS.getPropertyValue(dummy, "paddingLeft")) || 1) / measurement; /* GET */
  
                                  sameRatioIndicators.myParent.removeChild(dummy);
                              } else {
                                  unitRatios.emToPx = callUnitConversionData.lastEmToPx;
                                  unitRatios.percentToPxWidth = callUnitConversionData.lastPercentToPxWidth;
                                  unitRatios.percentToPxHeight = callUnitConversionData.lastPercentToPxHeight;
                              }
  
                              /***************************
                                 Element-Agnostic Units
                              ***************************/
  
                              /* Whereas % and em ratios are determined on a per-element basis, the rem unit only needs to be checked
                                 once per call since it's exclusively dependant upon document.body's fontSize. If this is the first time
                                 that calculateUnitRatios() is being run during this call, remToPx will still be set to its default value of null,
                                 so we calculate it now. */
                              if (callUnitConversionData.remToPx === null) {
                                  /* Default to browsers' default fontSize of 16px in the case of 0. */
                                  callUnitConversionData.remToPx = parseFloat(CSS.getPropertyValue(document.body, "fontSize")) || 16; /* GET */
                              }
  
                              /* Similarly, viewport units are %-relative to the window's inner dimensions. */
                              if (callUnitConversionData.vwToPx === null) {
                                  callUnitConversionData.vwToPx = parseFloat(window.innerWidth) / 100; /* GET */
                                  callUnitConversionData.vhToPx = parseFloat(window.innerHeight) / 100; /* GET */
                              }
  
                              unitRatios.remToPx = callUnitConversionData.remToPx;
                              unitRatios.vwToPx = callUnitConversionData.vwToPx;
                              unitRatios.vhToPx = callUnitConversionData.vhToPx;
  
                              if (Velocity.debug >= 1) console.log("Unit ratios: " + JSON.stringify(unitRatios), element);
  
                              return unitRatios;
                          }
  
                          /********************
                             Unit Conversion
                          ********************/
  
                          /* The * and / operators, which are not passed in with an associated unit, inherently use startValue's unit. Skip value and unit conversion. */
                          if (/[\/*]/.test(operator)) {
                              endValueUnitType = startValueUnitType;
                          /* If startValue and endValue differ in unit type, convert startValue into the same unit type as endValue so that if endValueUnitType
                             is a relative unit (%, em, rem), the values set during tweening will continue to be accurately relative even if the metrics they depend
                             on are dynamically changing during the course of the animation. Conversely, if we always normalized into px and used px for setting values, the px ratio
                             would become stale if the original unit being animated toward was relative and the underlying metrics change during the animation. */
                          /* Since 0 is 0 in any unit type, no conversion is necessary when startValue is 0 -- we just start at 0 with endValueUnitType. */
                          } else if ((startValueUnitType !== endValueUnitType) && startValue !== 0) {
                              /* Unit conversion is also skipped when endValue is 0, but *startValueUnitType* must be used for tween values to remain accurate. */
                              /* Note: Skipping unit conversion here means that if endValueUnitType was originally a relative unit, the animation won't relatively
                                 match the underlying metrics if they change, but this is acceptable since we're animating toward invisibility instead of toward visibility,
                                 which remains past the point of the animation's completion. */
                              if (endValue === 0) {
                                  endValueUnitType = startValueUnitType;
                              } else {
                                  /* By this point, we cannot avoid unit conversion (it's undesirable since it causes layout thrashing).
                                     If we haven't already, we trigger calculateUnitRatios(), which runs once per element per call. */
                                  elementUnitConversionData = elementUnitConversionData || calculateUnitRatios();
  
                                  /* The following RegEx matches CSS properties that have their % values measured relative to the x-axis. */
                                  /* Note: W3C spec mandates that all of margin and padding's properties (even top and bottom) are %-relative to the *width* of the parent element. */
                                  var axis = (/margin|padding|left|right|width|text|word|letter/i.test(property) || /X$/.test(property) || property === "x") ? "x" : "y";
  
                                  /* In order to avoid generating n^2 bespoke conversion functions, unit conversion is a two-step process:
                                     1) Convert startValue into pixels. 2) Convert this new pixel value into endValue's unit type. */
                                  switch (startValueUnitType) {
                                      case "%":
                                          /* Note: translateX and translateY are the only properties that are %-relative to an element's own dimensions -- not its parent's dimensions.
                                             Velocity does not include a special conversion process to account for this behavior. Therefore, animating translateX/Y from a % value
                                             to a non-% value will produce an incorrect start value. Fortunately, this sort of cross-unit conversion is rarely done by users in practice. */
                                          startValue *= (axis === "x" ? elementUnitConversionData.percentToPxWidth : elementUnitConversionData.percentToPxHeight);
                                          break;
  
                                      case "px":
                                          /* px acts as our midpoint in the unit conversion process; do nothing. */
                                          break;
  
                                      default:
                                          startValue *= elementUnitConversionData[startValueUnitType + "ToPx"];
                                  }
  
                                  /* Invert the px ratios to convert into to the target unit. */
                                  switch (endValueUnitType) {
                                      case "%":
                                          startValue *= 1 / (axis === "x" ? elementUnitConversionData.percentToPxWidth : elementUnitConversionData.percentToPxHeight);
                                          break;
  
                                      case "px":
                                          /* startValue is already in px, do nothing; we're done. */
                                          break;
  
                                      default:
                                          startValue *= 1 / elementUnitConversionData[endValueUnitType + "ToPx"];
                                  }
                              }
                          }
  
                          /*********************
                             Relative Values
                          *********************/
  
                          /* Operator logic must be performed last since it requires unit-normalized start and end values. */
                          /* Note: Relative *percent values* do not behave how most people think; while one would expect "+=50%"
                             to increase the property 1.5x its current value, it in fact increases the percent units in absolute terms:
                             50 points is added on top of the current % value. */
                          switch (operator) {
                              case "+":
                                  endValue = startValue + endValue;
                                  break;
  
                              case "-":
                                  endValue = startValue - endValue;
                                  break;
  
                              case "*":
                                  endValue = startValue * endValue;
                                  break;
  
                              case "/":
                                  endValue = startValue / endValue;
                                  break;
                          }
  
                          /**************************
                             tweensContainer Push
                          **************************/
  
                          /* Construct the per-property tween object, and push it to the element's tweensContainer. */
                          tweensContainer[property] = {
                              rootPropertyValue: rootPropertyValue,
                              startValue: startValue,
                              currentValue: startValue,
                              endValue: endValue,
                              unitType: endValueUnitType,
                              easing: easing
                          };
  
                          if (Velocity.debug) console.log("tweensContainer (" + property + "): " + JSON.stringify(tweensContainer[property]), element);
                      }
  
                      /* Along with its property data, store a reference to the element itself onto tweensContainer. */
                      tweensContainer.element = element;
                  }
  
                  /*****************
                      Call Push
                  *****************/
  
                  /* Note: tweensContainer can be empty if all of the properties in this call's property map were skipped due to not
                     being supported by the browser. The element property is used for checking that the tweensContainer has been appended to. */
                  if (tweensContainer.element) {
                      /* Apply the "velocity-animating" indicator class. */
                      CSS.Values.addClass(element, "velocity-animating");
  
                      /* The call array houses the tweensContainers for each element being animated in the current call. */
                      call.push(tweensContainer);
  
                      /* Store the tweensContainer and options if we're working on the default effects queue, so that they can be used by the reverse command. */
                      if (opts.queue === "") {
                          Data(element).tweensContainer = tweensContainer;
                          Data(element).opts = opts;
                      }
  
                      /* Switch on the element's animating flag. */
                      Data(element).isAnimating = true;
  
                      /* Once the final element in this call's element set has been processed, push the call array onto
                         Velocity.State.calls for the animation tick to immediately begin processing. */
                      if (elementsIndex === elementsLength - 1) {
                          /* Add the current call plus its associated metadata (the element set and the call's options) onto the global call container.
                             Anything on this call container is subjected to tick() processing. */
                          Velocity.State.calls.push([ call, elements, opts, null, promiseData.resolver ]);
  
                          /* If the animation tick isn't running, start it. (Velocity shuts it off when there are no active calls to process.) */
                          if (Velocity.State.isTicking === false) {
                              Velocity.State.isTicking = true;
  
                              /* Start the tick loop. */
                              tick();
                          }
                      } else {
                          elementsIndex++;
                      }
                  }
              }
  
              /* When the queue option is set to false, the call skips the element's queue and fires immediately. */
              if (opts.queue === false) {
                  /* Since this buildQueue call doesn't respect the element's existing queue (which is where a delay option would have been appended),
                     we manually inject the delay property here with an explicit setTimeout. */
                  if (opts.delay) {
                      setTimeout(buildQueue, opts.delay);
                  } else {
                      buildQueue();
                  }
              /* Otherwise, the call undergoes element queueing as normal. */
              /* Note: To interoperate with jQuery, Velocity uses jQuery's own $.queue() stack for queuing logic. */
              } else {
                  $.queue(element, opts.queue, function(next, clearQueue) {
                      /* If the clearQueue flag was passed in by the stop command, resolve this call's promise. (Promises can only be resolved once,
                         so it's fine if this is repeatedly triggered for each element in the associated call.) */
                      if (clearQueue === true) {
                          if (promiseData.promise) {
                              promiseData.resolver(elements);
                          }
  
                          /* Do not continue with animation queueing. */
                          return true;
                      }
  
                      /* This flag indicates to the upcoming completeCall() function that this queue entry was initiated by Velocity.
                         See completeCall() for further details. */
                      Velocity.velocityQueueEntryFlag = true;
  
                      buildQueue(next);
                  });
              }
  
              /*********************
                  Auto-Dequeuing
              *********************/
  
              /* As per jQuery's $.queue() behavior, to fire the first non-custom-queue entry on an element, the element
                 must be dequeued if its queue stack consists *solely* of the current call. (This can be determined by checking
                 for the "inprogress" item that jQuery prepends to active queue stack arrays.) Regardless, whenever the element's
                 queue is further appended with additional items -- including $.delay()'s or even $.animate() calls, the queue's
                 first entry is automatically fired. This behavior contrasts that of custom queues, which never auto-fire. */
              /* Note: When an element set is being subjected to a non-parallel Velocity call, the animation will not begin until
                 each one of the elements in the set has reached the end of its individually pre-existing queue chain. */
              /* Note: Unfortunately, most people don't fully grasp jQuery's powerful, yet quirky, $.queue() function.
                 Lean more here: http://stackoverflow.com/questions/1058158/can-somebody-explain-jquery-queue-to-me */
              if ((opts.queue === "" || opts.queue === "fx") && $.queue(element)[0] !== "inprogress") {
                  $.dequeue(element);
              }
          }
  
          /**************************
             Element Set Iteration
          **************************/
  
          /* If the "nodeType" property exists on the elements variable, we're animating a single element.
             Place it in an array so that $.each() can iterate over it. */
          $.each(elements, function(i, element) {
              /* Ensure each element in a set has a nodeType (is a real element) to avoid throwing errors. */
              if (Type.isNode(element)) {
                  processElement.call(element);
              }
          });
  
          /******************
             Option: Loop
          ******************/
  
          /* The loop option accepts an integer indicating how many times the element should loop between the values in the
             current call's properties map and the element's property values prior to this call. */
          /* Note: The loop option's logic is performed here -- after element processing -- because the current call needs
             to undergo its queue insertion prior to the loop option generating its series of constituent "reverse" calls,
             which chain after the current call. Two reverse calls (two "alternations") constitute one loop. */
          var opts = $.extend({}, Velocity.defaults, options),
              reverseCallsCount;
  
          opts.loop = parseInt(opts.loop);
          reverseCallsCount = (opts.loop * 2) - 1;
  
          if (opts.loop) {
              /* Double the loop count to convert it into its appropriate number of "reverse" calls.
                 Subtract 1 from the resulting value since the current call is included in the total alternation count. */
              for (var x = 0; x < reverseCallsCount; x++) {
                  /* Since the logic for the reverse action occurs inside Queueing and therefore this call's options object
                     isn't parsed until then as well, the current call's delay option must be explicitly passed into the reverse
                     call so that the delay logic that occurs inside *Pre-Queueing* can process it. */
                  var reverseOptions = {
                      delay: opts.delay,
                      progress: opts.progress
                  };
  
                  /* If a complete callback was passed into this call, transfer it to the loop redirect's final "reverse" call
                     so that it's triggered when the entire redirect is complete (and not when the very first animation is complete). */
                  if (x === reverseCallsCount - 1) {
                      reverseOptions.display = opts.display;
                      reverseOptions.visibility = opts.visibility;
                      reverseOptions.complete = opts.complete;
                  }
  
                  animate(elements, "reverse", reverseOptions);
              }
          }
  
          /***************
              Chaining
          ***************/
  
          /* Return the elements back to the call chain, with wrapped elements taking precedence in case Velocity was called via the $.fn. extension. */
          return getChain();
      }