Generalize Part HTML rendering #561
Description
Currently, Verso parts are rendered to HTML inside a bare <section> tag. In writing leanprover/reference-manual#599, it would have been useful, as a verso document author, to be able to attach a class="no-vale" attribute to that tag.
It might also be useful for other reasons to generally influence the attributes of this tag, or maybe even to inject other content before or after it. This issue proposes deciding on what extensibility is appropriate, and adding it to part HTML rendering, and/or other output formats as appropriate.