Divider line in list fields

[Alan Gayne]

I may have missed it in the documentation, but is there any way to put a 
true non
selectable divider line (similar to those in a pull down menu) in a list
field?

I've tried using the " - " character that works in the menu - but all I 
get
is a " - "  -  duh!

ALSO, what is the correct command to de-select all of the selected lines 
in a list field?

Thanks in advance

Alan