From Xojo Documentation
Used to organize controls on hidden panels. Only the controls on the current panel are visible to the user. This control does not display a user interface at run-time.
The DesktopPagePanel control allows you to add controls to panels, just as you add controls to DesktopTabPanels. The difference is that the DesktopPagePanel control itself is not visible in your built application. Only the controls on the currently selected panel are visible. You change the displayed panel by changing the SelectedPanelIndex property. PagePanels cannot be embedded inside PagePanels.
You get or set the panel on which a control is located via the PanelIndex property of the DesktopControl class. The first panel is numbered zero.
In the IDE, you can add, insert, delete, reorder and navigate from panel to panel, just like a DesktopTabPanel. When building an interface using the DesktopPagePanel, you can take advantage of the Control Hierarchy, discussed in the section on the DesktopUIControl object.
The following line of code moves a DesktopListBox from its current panel to the second panel of a DesktopPagePanel.