The parameter, when set to preferred, returns only preferred values; when set to normal, returns only normal values; when set to deprecated, returns only deprecated values. If the parameter is set to best, it returns preferred values if present, otherwise normal values. Any parameter value beginning with "p" is "preferred"; any parameter value beginning with "n" is "normal"; any parameter value beginning with "d" is "deprecated"; any parameter value beginning with "b" is "best". Combinations of values are allowed, e.g. returns all the preferred and normal values (which is the default), although "best" overrides any other parameters.