The ctlid parameter is often set to zero, which causes EVENTWAIT to initially put the focus on the first control within the specified parentid. On exit, it will be automatically set to the ID of the control that last had the focus (or was just clicked on). Setting the ctlid to a specific control ID will cause the focus to start there.
If the specified ctlid does not exist, EVENTWAIT returns exitcode 99. Also note that if ctlid does exist, but is not in the group you specified by parentid, then the results might be unpredictable.
History
2011 February, A-Shell 5.1.1205: You can now pass alphanumeric IDs for the parentid and ctlid parameters. This eliminates one of the most common excuses for needing a numeric control ID. Note, however, that the updated ctlid parameter will be returned as a number (although formatted as a string if you pass a string parameter). This shouldn't make any difference to your application as a string-formatted numeric control ID may be used anywhere an alphanumeric control ID may be used.
