Setting the tab order
A widget's focus determines that widget's activity available using keyboard. Focus is related to widgets displayed in the form's data view. Exactly one form widget can have focus at the same time. The most frequent use of focus is text entry (when a given text field is active, i.e. it is focused). An other example is a button widget - when focused, it is possible to “press” it using the Enter or Space key instead of a mouse button.
There are a few methods of making the widgets active (moving the focus to the widget): clicking with a mouse button, rotating the mouse wheel over the widget, or using the Tab key. The latter method is often used because of its speed and convenience for users. Availability of the focusing methods is controlled by Focus Policy property of a given widget.
There is a relationship between focusing (activating) widgets using Tab key and tab order setting of a form. After pressing the Tab key, the next widget should be focused, so the form should know about the tab order.