for - tinnitus - mitigation via the Clarify - sensory substitution - vibrate at the same time as the sound - to decrease amplitude of tinnitus - Neosensory - David Eagleman

for - BEing journey - consumer electronic device - the Clarify - sensory substitution - auditory to vibration compensation - for high frequency hearing loss in older people - Neosensory - David Eagleman

• sensory substitution - The Clarify - Performs better than conventional hearing aids - Neosensory - David Eagleman

for - question - the brain believes what it imagines - clarify - John Churchill

This makes it sound like there is an HTML element with a tag name of <toc nav> rather than <nav epub:type="toc"> (which seems to be what's intended).

The landmarks example farther down is clearer--though the wording there of "the landmark nav element" is equally confusing.

There remains only a nav element, but of varying types.

This line is confusing because the actor (author or reading system) is unclear. The following two lines are much clearer on what actor is being restricted by this specification.

This line feels specific to the Reading System requirements. Consequently, perhaps it's best to integrate it into the sentence just following.

Link resolve to any defined algorithms for resolving resources within an EPUB.

This requirement is clearer than the one just previous and also seems to obviate the earlier one.

However, this one is confusing limiting the textual expression to just the title attribute, and also being vague of which element is associated to the MUST--is it this surrounding a or span? or the contained "embedded content" element?

Implied requirement? When is this necessary and what does the concatenation and normalization?

Where is this "visual display" taking place? Is this when the document is viewed as a spine element? or is this when the content is extracted and presented by the Reading System?

Rephrase "while a child span element" and perhaps move to it's own sentence parallel to the "A child a element"

Link to this, if defined.

Is "non-browser context" defined? or its inverse?

It's not clear if "browser" here is equivalent to "Reading System" or to a Web browser or something else.

Used by? It's not clear who the actor is here, the author/developer of the EPUB or the Reading System.

Is the "table of contents" a specific type of custom control? If so, a link would help here.

But it does have effect on "spine rendering"? Perhaps add a link for spine rendering.

Is "data island" a specific, defined thing from a previous EPUB spec or another adjacent spec?

Link to a definition of "custom control" if one exists.

Not sure what a "typical XML data island" is either...so some links or even rewording (or removing?) might help others unfamiliar with the phrase.