The tab key and shift+tab keys have no effect when the controls in the dialog box do not have the WS_TABSTOP style. The system looks for this style as it searches for the next control in the dialog box to receive the input focus.
When the user presses tab or shift+tab, the system first determines whether the control having the input focus processes these keys. It sends the control a WM_GETDLGCODE message, and if the control returns DLGC_WANTTAB, the system passes the keys to the control. Otherwise, the system uses the GetNextDlgTabItem function to locate the next control that is visible, not disabled, and that has the WS_TABSTOP style. The search starts with the control currently having the input focus and proceeds in the order in which the controls were created — that is, the order in which they are defined in the dialog box template. When the system locates a control having the required characteristics, the system moves the input focus to it.
An application can also use GetNextDlgTabItem to locate controls having the WS_TABSTOP style. The function retrieves the window handle of the next or previous control having the WS_TABSTOP style without moving the input focus.