With Flash deprecation, it might be the case that browsers no longer implement plugins, and as such we could remove some of the spec complexity around them.

Note, however, that we do need to keep enough to allow rendering of PDFs, and to allow rendering of HTML pages (and other supported content types) in embed and object. So it's not like we can completely gut the embed and object sections.

And, it looks like at the time of #3958, Chrome treated PDFs as plugins. So maybe we can't remove much.

Anyway, some candidates for removal:

• Page load processing model for plugin documents, under the assumption that PDFs count as inline content that doesn't have a DOM (TODO test if that assumption holds; the above indicates it might not in Chrome)
• Sandboxing infrastructure for plugins, but see Interop: pdf might or might not render in a sandboxed iframe (depending on a browser) #3958 for PDF-related concerns
• Description of plugins
• NavigatorPlugins and friends, but see Consider a standardized way to detect PDF in HTML? #3462; PDF support might end up living here in existing browsers.
• embed and especially object could likely be simplified to be more like iframe.
• The param element might be able to be totally neutered and moved to the obsolete section.

The param simplification likely holds even if PDF ends up staying around as a plugin. (And in turn we can close #387.)