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Every widget (except the root window) has a parent. However,
the child widget does not actually appear on the screen until
it is gridded with the .grid() method.
So, to give the illusion that many different pages can
appear in the same space, each page inside a PageTurner
is a single child widget of its .bodyFrame attribute, but only one is gridded
at any given time.
The first time a new page widget is added to a PageTurner
by calling its .addPage()
method, the new page is gridded inside the .bodyFrame at row 0, column 0, at which
point it appears on the screen.
From then on, whenever we want to present a different
page, we can make the current page invisible by calling
its .grid_forget() method. This
removes that child from the screen, but it is still
registered as a child of .bodyFrame, and can be put back anytime by
calling its .grid() method. (In
this respect .grid_forget()
differs from .grid_remove(),
which destroys the child widget altogether.)