What is the significance of the double brackets for the [[prototype]] property in JavaScript?

Question

I know that every JavaScript object has an internal property called [[Prototype]]. Some implementations allow access to it via a property called __proto__

Answer 1

The reason it's in brackets is to denote that it's a private property. The brackets themselves are never used in code anywhere.

As you pointed out, some implementation provide access to that private property under __proto__, but it's non-standard.