Question on structure of Segwit part of transaction

[jansma43]

Can anyone tell me where I can find a full technical description of the changes in the structure of the bitcoin blockchain for Segwit?

A few years ago I created my personal blockchain browser. Now I am trying to update this browser for Segwit. I have limited knowledge of the cryptography and I just try to analyse the blockchain data. I see that in a Segwit transaction for every transaction input there is a Segwit part. This Segwit part seems to have three different structures identified by the value of the first byte: 0, 2 or 4. Structure 0 has zero length Segwit part, 2 has two variable fields Segwit data and 4 has three variable fields Segwit data. Can someone explain the meaning of these three different Segwit data structures?