       cindex string indexExpr
              Returns  the  character  indexed  by the expression
              indexExpr (zero based) from string.

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

              This command is provided by Extended Tcl.
