Regarding the 'Search' functionality:

1) Special symbols such as $ now are searchable (without specifically adding quotes) -- excellent, great improvement!!

2) Searching WITH quotes fails to perform same search:
Due to above, searching both $d and $data (without quotes) works correctly. Now notice the failure of the same search with quotes: "$d" (no $data results at all) and "$data" (appropriate result 17 items down).

3) When the search query contains quotes, the summary at the top of the page fails to decode the special characters ("). For example searching "$data" will display at head of result page:
Matches in text: 1 - 20 of 76 for "$data". (.00029s)  

4) Following a link from the Search Results page doesn't allow for respecting the in-page 'Back' button. It's unclear if this is the intended use of 'Back'. By landing on a doc from search, using the 'Back' button does not return the user to the previously used page (the search results), but instead goes to a higher level in tree-view.

Yes, exactly. Thanks.

Preferably there is some smooth way of backtracing these bread crumb trails that are maintained in that left pane. Can the back button smoothly transition back to the higher level tree-view? Essentially as I drill down the high level view of the documentation books, can each section and subsection be displayed while leaving the highest level of books still within browsable view? I don't see why this concept of a 'book' needs to be restrictive against transparently browsing multiple topics among multiple books.

Browsing (top-level) tree-view of topics is not possible when you've drilled into a section.

Browse in left pane to a book and section to view. Clicking into that section brings you to the doc page, however it also restricts the tree-view in the left pane only to the current book. To further browse all docs, you need to go 'back' (which removes the doc you've been viewing!).

I'd want the possibility to browse in the left pane to a new section without losing my view of the actual page in docs in the right pane. Often it is helpful to keep the view of the actual doc page while browsing to your next (related) topic.

Completely agree, and one of the first shortcomings I noticed. Search bar should ALWAYS be an option an any page, at any time.