This flag allows the focus to be moved (via the keyboard Arrows and Tab/Shift+Tab) into child subgroups of the parentid. Otherwise keyboard navigation is limited to the immediate group. For example, in the sample dialog above (see parentid) there are three or four separate groups in the dialog. If you start an eventwait with parentid set to one of them but the EVW_DESCEND flag not set, the user will be able to navigate around the controls in that group, but not leave the group (except by clicking or some other event that triggers an exitcode). This might be useful if you wanted to do some validation logic on the group as a whole before moving to another group. On the other hand, if you wanted to allow the user to navigate around all of the groups without requiring program intervention, then you could set the parentid to the ID of the dialog itself and set the EVW_DESCEND flag.