EVW_NOWRAP
This option controls what happens when keyboard navigation commands (Arrows, Tab, Shift+Tab) are used to move the focus around within a group of controls and you hit the "edge". If the flag is not set, then the focus will "wrap" around to the first control in the group. Otherwise, the eventwait operation will exit, setting EXITCODE 3 (up, left) or 5 (down, right) depending on which direction the group was exited. (The ctlid parameter will also be set to identify the last focused control, so the distinction between exitcode 3 and 5 may not be that important.)
As an example, consider the Tab Control Example dialog above, which features a groupbox containing three buttons. In the default case, without EVW_NOWRAP, hitting the Left/Right Arrows, or Tab/Shift+Tab keys, will just move the focus around in a circle between the buttons. The user will have to click on one, or hit Enter to exit from the eventwait. If the user wanted to edit one of the fields in the tab pane, they could click the "Edit" button. As an alternative, you could use the EVW_NOWRAP flag, in which case, merely using the arrow keys would trigger an exit from the eventwait, allowing the program to refocus on one of the edit fields. (See EVW_SIBLINGS and EVW_DESCEND flags for other approaches to allowing the user to navigate around the dialog.)
