If an application uses notebook controls that contain tab pages, the default condition is for the application to draw the contents of the tab each time a tab page is displayed. This situation applies particularly if the content of the tab is not one of the supported formats.

The notebook control window procedure generates this message and sends it to its owner, informing the owner that the content of a tab is to be drawn. The owner is given the opportunity to draw the content of the tab and to indicate that the content of the tab has been drawn or that the notebook control is to draw it. To indicate that the notebook control is to draw the content of the tab, the owner sends either a BKM_SETTABTEXT or a BKM_SETTABBITMAP message to the notebook control.