       lvarpop var ?indexExpr? ?string?
              The  lvarpop  command  pops  (deletes)  the element
              indexed by the expression indexExpr from  the  list
              contained  in  the variable var.  If index is omit-
              ted, then 0 is assumed.  If string,  is  specified,
              then the deleted element is replaced by string. The
              replaced or  deleted  element  is  returned.   Thus
              ``lvarpop  argv  0''  returns  the first element of
              argv, setting argv to contain the remainder of  the
              string.

              If  the expression indexExpr starts with the string
              end, then end is replaced with  the  index  of  the
              last element in the list.  If the expression starts
              with len, then len is replaced with the  length  of
              the list.

              This command is provided by Extended Tcl.
