Interface to code that manages versions of a Page. Initially a page has a version number of 0, indicating that it is in its original state. When one or more changes are made to the page, we arrive at version 1.

During a request cycle, just before a change is about to occur, beginVersion() is called, followed by one or more calls to componentAdded(), componentRemoved() or componentModelChanging(). If beginVersion() is called by the framework during a given request cycle, a balancing endVersion() call will occur at the end of the request cycle. However, if no changes occur to a page during a request cycle, none of these methods will be called.

Once version information has been added to a version manager, versions can be retrieved by number using getVersion(int). Since version 0 is the first version of a page, calling getVersion(0) will retrieve that version.

The current version number (the number of the newest available version) of a page can be retrieved by calling getCurrentVersionNumber().