I am reading and taking notes on the HTML specifications for 100 days as part of #The100DayProject. Read the initial intent/backstory. I am a Microsoft employee but all opinions, comments, etc on this site are my own. I do not speak on behalf of my employer, and thus no comments should be taken as representative of Microsoft's official opinion of the spec. Subsections not listed below were read without comment.
Currently reading in 18.104.22.168 Paragraphs.
A "paragraph" in the spec connotes more than the
<p> tag. In fewer words, it is a chunk of text (phrasing content) discussing a discreet idea. A paragraph could also be, for the spec's purposes, an address, a part of a form, a byline, or a poem stanza.
Some elements (a, ins, del, map) can "straddle" paragraphs, and so the UA needs to ignore these elements when interpreting which portions of phrasing content are individual "paragraphs". Judging from the first example given, this seems like a protection against messy markup.
Reading the other examples starts to get like one of those puzzles where you have to guess how many triangles there are in an abstract design. Bananas!