Idea: Document tree navigation commands UI

[Krzysztof Żelechowski]

Chrome should have document tree navigation commands to navigate to page
links: NEXT [2], PREV, START [3], CONTENTS, SEARCH [4] and HELP [5]. This can
probably be achieved by an extension; however, I was unable to find any Chrome
extension to do that.

Motivation: Providing users with a means to follow hyperlinks created using
the link element [1].

The commands may be attached to a drop down list and provide keyboard
shortcuts, e.g. Ctrl+CursorKey, Ctrl+F3, Ctrl+F1.

It is somewhat possible to implement this feature using in-page Javascript;
however:
1. in-page Javascript is not always allowed
2. it is annoying to have navigation hovering over content
3. if these commands do not hover over content, it will be harder to find them
4. in-page Javascript cannot read HTTP headers

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[1] <URL: https://html.spec.whatwg.org/multipage/semantics.html#providing-users-with-a-means-to-follow-hyperlinks-created-using-the-link-element >
[2] <URL: https://html.spec.whatwg.org/multipage/links.html#link-type-next >
[3] <URL: https://microformats.org/wiki/existing-rel-values#formats >
[4] <URL: https://html.spec.whatwg.org/multipage/links.html#link-type-search >
[5] <URL: https://html.spec.whatwg.org/multipage/links.html#link-type-help >