Your ClearCase admins will have created a trigger on pre-op checkin. What it's called is entirely up to them.
You can find out what triggers are on the VOB by running
cleartool lstype -kind trtype -l -invob <vob_tag>
in clearcase, while checking in an element a prompt is made to user to enter the doc_status attribute. how is this done?
Which trigger is invoked to prompt the user to enter the doc_status during check-in?