drop-down list - working with default value

Hello,

we have drop down list with enabled option "Allow Custom Text Entry" (combo-box). We need to display as a default value text : "-- Choose or Type --".

After the drop down list get focus, we need to make the field empty, so the user does not need to delete the text "-- Choose or Type --".

Then, when user does not choose or type anything and exits the drop-down list, we need to display "-- Choose or Type --" again.

If the only option is to have the value "-- Choose or Type --" as one of list items, we need, that it have value null, empty string or false.

Is there a way to do this ?

The best result I get is when in enter event is set this.rawValue = ''  -> field becomes empty but I have not fond the way how to set again the value to "-- Choose or Type --". Even calling xxx.selectedIndex=0; or xxx.setItemState(0,true); in exit action does nothing.

I know it would work, if the "-- Choose or Type --" has value e.g. '000', but this is quite big change for validation scripts, that we cannot accept in this phase of project.

Thanks for any advice.