pass through input, e.g., quantity to allowed class if only one specified
pass through input, e.g., quantity to allowed class if only one specified

MSeifert04/astropy,lpsinger/astropy,pllim/astropy,mhvk/astropy,saimn/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,stargaser/astropy,dhomeier/astropy,pllim/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,astropy/astropy,larrybradley/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,MSeifert04/astropy,stargaser/astropy,astropy/astropy,MSeifert04/astropy,aleksandr-bakanov/astropy,mhvk/astropy,saimn/astropy,dhomeier/astropy,saimn/astropy,larrybradley/astropy,StuartLittlefair/astropy,mhvk/astropy,larrybradley/astropy,stargaser/astropy,dhomeier/astropy,StuartLittlefair/astropy,lpsinger/astropy,saimn/astropy,larrybradley/astropy,stargaser/astropy,aleksandr-bakanov/astropy,astropy/astropy,lpsinger/astropy,mhvk/astropy,pllim/astropy,astropy/astropy,astropy/astropy,dhomeier/astropy,pllim/astropy,saimn/astropy,dhomeier/astropy,lpsinger/astropy,MSeifert04/astropy,mhvk/astropy,pllim/astropy