Per-document style-sheet

I've now set up a few different stylesheets that I use with different kinds of documents. For example, notes I'm writing for lectures are more tightly formatted, with a smaller font, than something I'm doing as an article. It's bit of a hassle to have to go into the prefs to switch from one to the other, so I'm requesting either:

1. documents can have their own stylesheets; i.e., they can be set to over-ride the current default. This could be done by allowing the stylesheet to be set in the YAML header, for example, as pandoc does.
2. Easy access to the stylesheets in the menu, instead of going into the preferences. Something like File>Stylesheet>[list of stylesheets]. Or this would be great in the toolbar.

The two are not mutually exclusive of course.

The issue names YAML headers for per-document stylesheets and a File > Stylesheet menu or toolbar control, but it does not identify files or tests. Start by locating the existing stylesheet preference and document-loading code, then determine which of the two requested approaches is in scope. Done means a document can select its own stylesheet or stylesheets are quickly selectable, with coverage for the chosen behavior.