Sorry, I relied too much on taginfo displaying the wiki entry more promptly. 

I would be grateful if the existing keys were mentioned in the proposal and if the suggestion with library:for were also mentioned as a possible alternative (however, I haven't had time to read all the contributions in full yet). One reason against for would be, for example, that here it is usually gender (clothes:for) or age (social_facility:for) that is differentiated.