TabOrder property

TabOrder is a zero-based integer that determines the order in which the viewer is visited when the user repeatedly presses Tab. The lowest TabOrder in the same parent receives focus first, and Shift+Tab moves backwards through the sequence.

In a typical PDF reader window the viewer is usually given TabOrder := 0 so that pressing Tab after the form opens immediately enables keyboard navigation of the document. Toolbar buttons, sidebar lists and search boxes are then assigned higher values so they participate in the cycle without stealing focus on startup.

The property is meaningful only when TabStop is True — controls with TabStop = False are skipped by the tab cycle regardless of TabOrder. Re-assigning TabOrder at run-time renumbers the siblings automatically, just like in any other TWinControl.

• Persistent property — saved to the form file together with TabStop.
• Supported identically by VCL and Lazarus LCL.
• Each parent maintains its own tab cycle; nesting the viewer inside a panel groups it with the other panel children rather than with the form's top-level controls.
• For accessibility audits, ensure the cumulative tab path through your reader UI reaches the document area before help dialogs — users navigating only by keyboard should be able to view pages before exploring secondary windows.