[InJen]

in Oxford online dictionary, there is a sentence:

As was his custom, he knocked three times.

has ellipsis been used in this sentence?
if yes, what is the lengthened form of the sentence?

[susan53]

No - this is subject verb inversion, not ellipsis. the use of inversion after "as" has already been discussed as part of a longer question, which you can find here : Emerson

[InJen]

sorry for having omitting that thread

the first time read it I was none the wiser. I have read it once more, and your answer is really excellent. Thank you very much indeed.