Determines which tab of a tab set control is currently selected.
property TabIndex: Integer;
The value of TabIndex can be from -1 to one less than the number of Tabs. TabIndex is an index in the Tabs collection property: a value of 0 indicates the first tab in the tab set control, 1 is the second tab, and so on. If no tabs are selected, TabIndex has a value of -1.
When a value is assigned to TabIndex, OnChange event occurs, just as if the user had clicked on a tab.