Silas 2005.08.23 - Showing sublists in a listbox can be not so pratical. See:

 listbox .l -listvariable mylist
 pack .l
 set  listone {item1 item2}
 set listtwo {item3 item4}
 set listthree {item5 {sublist sublist} item6}
 lappend mylist $listone
 lappend mylist $listtwo
 lappend $listthree
 lappend mylist $listthree

I could use join or another function to do it better, but suppose you will you the variable (in this case, mylist) in the code. You can't just modify your variable. My solution is using two lists. One to show in the listbox and another to use in the code. Always that the original variable is modified, it is possible to join everything again to the new variable.

put an example here