Adds elements to the pool of item elements of the container, but does sort, filter or layout. See [Adding items](adding-items.html) for more details. The argument within the callback is the group of elements that were added.
Adds elements via `addItems` method, then triggers `layout` just for those new elements. Useful for Infinite Scroll. See [Adding items](adding-items.html) for more details.
Appends elements to container, adds items to via `addItems` method, and then triggers `reLayout` method so new elements are properly filtered, sorted and laid-out. See [Adding items](adding-items.html) for more details.
`layout` will only position specified elements, and those elements will be positioned at the end of layout. Whereas `reLayout` will position all elements in the Isotope widget.