Context

Function and field execute on current context, and, function body and field body execute on child context.

{
    "value": "hello",
    "child": {
        "value": "world"
    }
}

In example, $value is String of "hello" and $child is Object. $child[/*here*/]'s here is child context, so $child[$value]'s $value is String of "world"

Not necessarily, all function body executes on child context. some function's body executes on current context or parent context, need to remember see function document.