ControlContext :: displayLevel - Display level property
The display level property contains the display level currently set for the control. Display levels are used for tab-controls and virtual tab-controls in order to display different forms in the same area. Display levels might also be assigned to controls in a form in order to display different controls according to the display level currently set. Controls with display level 0 are always displayed.
Display levels might be assigned to fields, buttons and constants. The display level might be changed in different ways by calling setDisplayLevel().
The display level activated may differ from the display level defined for the control, i.e. the display level, on which the control becomes visible (showLevel()).
The display level is be a value greater or equal to zero. The value must not exceed the number of display levels in the control (e.g. the number of tabs in a tab control).
Display level 0 causes hiding all controls except those defined on level 0, which are visible on any display level.
Implementation details
The function returns the display level set for the control. For virtual controls, widget stacks or tab controls the display level refers to the active tab.