The new per-page CSS feature is great, but I think it would be useful if <body>
had classes for all pages in the current page hierarchy.
For example, if you had a page foo/bar/meh, instead of having one <body> class
of "page-foo_bar_meh", you'd have three: "page-foo page-foo_bar
page-foo_bar_meh". This would be useful for places like StrategyWiki
(http://strategywiki.org/), where guides are organised using sub-pages.
I suppose this is an extension of bug #5795.