webMethods 10.1 REST Resources how to use various source

Find the attached image for understanding the various sources for REST Resource v2.
I tried fiding the details for each Source.
But still strugelling to find details of what these source do.
What happens when a particular source is selectred.

What I have found as of now, is when FORMDATA source is selected, the JSON input is read as jsonbytes.
My purpose is to read the json variables in the REST Resource v2 in webMethods IS.