I think it's a naming convention that means nothing ;)

  1. Field1: { eq: 'SomeValue' },
  2. Field2: { notIn: ['Value1', 'Value2' ]}

I think it's quite common knowledge that double underscore is reserved for the system, but I'm open to ideas.

configurable is an option, it can potentially open a whole can of support worms 😄

people might have fields with two underscores not so uncommonly