WARNING - This post is NOW incorrect based on information surfaced later in this thread. page 104 of latest Dev Guide.

Another interesting point about Page.onEntry/onExit is that they are called exactly once, even if the page script is repeated.

so, for a page, logic is...

Just after page is loaded such that all GUI widgets are available,
remote does the equivalent of:

if (page.onEntry)
page.onEntry.call(thisPage);

Then, remote executes any script in the page, repeating if user desires based on pageInterval.

Then, just prior to leaving said page
remote does equivalent of :

if (page.onExit)
page.onExit.call(thisPage);