       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.
