Write docstrings for the propagation mixins
Write docstrings for the propagation mixins

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