ScrollPane has two properties:

prefViewportHeight
Specify the preferred height of the ScrollPane Viewport.

prefViewportWidth
Specify the preferred width of the ScrollPane Viewport.

They are used to determine size of visible area, that is width and height of control, minus size of scrollbars and borders. That is clear size of visible part of content.

Seems, such properties, at least as ReadOnly ones would be very useful, when you work inside callback (factory for page generation) and when you can clearly now, content of which size would be seen completely.

Seems, that is an idea if paginator, to devide content on fully visible parts.