[Drumstix42]

During runtime of the UI, the main window elements (Pet, Target, Inventory, Broker, Player, etc) all get put into the same "_ROOT" element in which they are located under. With this structure tree you can see how they are placed and how to access them via script:

_ROOT
   |- Target
      |- v0
      |- v1
      |- HighFantasyPetPage
      |- WindowFrame
   |- Pet
      |- WindowFrame
   |- Random window name
   |- Another random window name

I put a few examle Pages under those windows just to show how the tree looks as you go further in.

So let's say your Pet window's main page has an element of "OnShow".
Inside that element, you need to access your High Fantasy pet page (whatever the name might be). You'll need to travel backwards in the tree just one time (to reach the _ROOT) and then down into that pet page, and mark it visible:

Parent.Target.HighFantasyPetPage.visible=true

The "Parent." instructs the code to navigate backwards one time in the tree's hierarchy. If you needed to do it more than once, you would just continue:
Parent.Parent.Parent.Parent.WindowName.SubPage1.SubPage2.Page2Text.visible=true

And then do the opposite in a "OnHide" property:

Parent.Target.HighFantasyPetPage.visible=false