The spec should clarify whether or not document-wide (soon to be per-host) editing states such as of StyleWithCSS and DefaultParagraphSeparator to be reset when a new document is loaded.
IIUC, the HTML spec says that when you load a new document, the Document object is replaced entirely. Therefore, any state associated with it is replaced. I added a note to this effect. I also added that it gets reset on document.open(), which was not explicitly required anywhere before AFAICT.
This makes sense to me, thanks!