Users don't need to go thru a input map anymore to do things with painless. They can access _score, doc, ctx, _value etc directly, and those are first-class citizens and optimized to one degree or another to be fast, with any typing (e.g. map) we can use.

So typically this map in most cases only used to access params from the user Because of that I think we should name it exactly that, it makes usage intuitive:

script: "ctx._source.foo = params.bar"
lang: "painless"
params: { 
    bar: 'xxx' 
}

Also I updated some outdated syntax in various places to try to make things better.