       lvarpush var string ?indexExpr?
              The  lvarpush command pushes (inserts) string as an
              element in the list contained in the variable  var.
              The  element  is inserted before position indexExpr
              in the  list.  If  index  is  omitted,  then  0  is
              assumed.  If var does not exists, it is created.

              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.  Note the a value of end means insert the
              string before the last element.

              This command is provided by Extended Tcl.
