Why does accessing a field on a pointer to a struct work in rust?

I've noticed that, given a P<SomeStruct>, accessing fields of the SomeStruct directly on the pointer seems to work, and I'm not sure why that is. For example, this code compiles and works as expected (prints "1234"):

#![feature(rustc_private)]

extern crate syntax;
use syntax::ptr::P;

struct Baz {
    id: String,
}

fn foo() {
    let mut struct_pointer: P<Baz> = P(Baz {
        id: "1234".to_string(),
    });
    println!("{}", struct_pointer.id);
}

What language feature is allowing me to access the id field on the struct_pointer binding? Dereferencing? Coercion? And is there any way to tell that this sort of thing will work by looking at the docs for P?