tabpanelindex is not for knowing what page of a tab panel is currently showing
its a property for an embedded control so it knows which tab, out of many, its on
tabindex is for knowing a controls tab order - again not for knowing what tab of a tab panel is showing
if you have lots of controls that are in the tab order then they will have a tab index (textfields, textareas, etc) http://documentation.xojo.com/index.php/RectControl.TabIndex