       keylget listvar ?key? ?retvar | {}?
              Return the value associated with key from the keyed
              list in the variable listvar.   If  retvar  is  not
              specified,  then  the value will be returned as the
              result of the command.  In this case, if key is not
              found in the list, an error will result.

              If retvar is specified and key is in the list, then
              the value is returned in the  variable  retvar  and
              the command returns 1 if the key was present within
              the list.  If key isn't in the  list,  the  command
              will  return  0, and retvar will be left unchanged.
              If {} is specified for retvar,  the  value  is  not
              returned,  allowing the Tcl programmer to determine
              if a key is present in a keyed list without setting
              a variable as a side-effect.

              If  key  is omitted, then a list of all the keys in
              the keyed list is returned.

              This command is provided by Extended Tcl.
