Non-Adverbial "as is"

I know the common adverbial usage of "as is" as in,
Leave it as is.

As a non-native English speaker I found a strange-to-me but common English usage of non-adverbial "as is" and sometimes also "as are/was/were", which I cannot find its listing in the dictionary and in my (basic) English grammar book. With my search in the Corpus of Contemporary American English, I was able to find 4 kinds of of non-adverbial "as is".

1. as is = like

Ride quality and straight-line speed are also impressive, as is the Pro 4's resistance to tread cuts.

Certainly, looks are a factor, as is overall vibe.

As is the case in many academic libraries, space is at a premium.

2. as is = as it is

As far as is possible, populations must want to move and must have active influence.

As much as is possible, we must leave our sorrows.

3. as is = as

We experienced attrition from year 1 to year 2, as is expected in multiyear studies.

4. as is = as well as being

As is well-known, Hawthorne himself was considered a very handsome, indeed, a beautiful.

My question, simply put, "What is this?".

Solution 1:

I think "as is" is often used as shorthand for: "as it currently is" or "the way things are now", though I cannot tell you the grammatical rules of why this came into being. This is how it is used in your defining example.