As witnessed below (as=?) [closed]

My research: Often in legal papers, above the space for the witness to sign happens to be written:

As witnessed below ...

Now, according to my extent of English I would expect something like "as a witness" or something.

Though what really bugs me is I cannot figure which defintion of "as" is being used here.

Please explain. I would be so grateful if you could cite the dictionary defintion as well.

Solution 1:

As witnessed below =

As is witnessed below =

As is testified to by me below. =

In the manner that is testified to by me below. =

All that is written above is in the manner that is testified to by me and, by my signature, I confirm this.