Typos, formatting, and clarity suggestions

[pes10k]

This issue is part of the PING privacy review w3cping/privacy-request#65

While reviewing the spec for the privacy review, I found a couple of non-substantive issues in the text, issues that aren't related to privacy concerns, but would help the reader in following along.

• Typo: "an (hypothetical)" -> "a (hypothetical)"
• Nit: caps consistancy. Should defined terms should either be title case (e.g., "IMSC Document Instance") or sentence case (e.g. "intermediate synchronic documents"), but switching between the two is confusing (since its not clear when its a reference to a document section or a term of art)
• Links: There are many terms used in the document that will not be familiar most readers. However, instead of linking to definitions for these terms, though, links are just given for the document containing the definitions. So, for example, currently the document has terms like "intermediate synchronic documents" link to same-document text saying "Intermediate Synchronic Document. See [ttml2].". With that "ttml2" link taking the reader to the top of the TTML2 spec. It would be more helpful to have "intermediate synchronic documents" link directly to the part of the TTML2 spec that defines "intermediate synchronic documents" (i.e., https://www.w3.org/TR/2018/REC-ttml2-20181108/#semantics-region-layout-step-1)

[palemieux]

@pes10k See #33

Re: title case, I tried to make the capitalization of defined terms consistent with their definition. The current trend is to avoid capitalization, lest we end-up with uppercase everywhere, and so some of the more recent terms, including those defined in this document are lowercase.

[pes10k]

I see, understood then. If thats the convention then, then I think #33 addresses the concern. Thanks!