YAML option to place a class on the body of a page

[dragonstyle]

maybe most can be accomplished by giving the site a specific id and then rely on styling. Is there a setting to add a class/id to the body tag of a site?

Using page-layout: custom get's me some of the way but I still can't target the header of the page specifically if I want to format it differently

I guess this is really a feature request to get a yaml metadata option for setting a class on the page (which allows implementation of special treatments without re-implementing partials)