A POP indicates a change to an arbitrary index in the history stack, such as a back or forward navigation. It does not describe the direction of the navigation, only that the current index changed.
Note: This is the default action for newly created history objects.
A PUSH indicates a new entry being added to the history stack, such as when a link is clicked and a new page loads. When this happens, all subsequent entries in the stack are lost.
A REPLACE indicates the entry at the current index in the history stack being replaced by a new one.
Actions represent the type of change to a location value.