I'm studying prototype and doing some testing, and I've decided to assign a method to the String object like this:

String.prototype.sel = function sel() {
    var elem = doc.querySelectorAll(this);
    if (elem.length == 1)
        return elem[0];

    return elem;
}

And when getting a console.log(String.prototype) and getting the method I created, I noticed that in [[Scopes]] I get 1: Global {window: Window..., what does [[Scopes]] mean?

Complete test:

String.prototype.sel = function sel() {
    var elem = document.querySelectorAll(this);
    if (elem.length == 1)
        return elem[0];

    return elem;
}

'[btnSend]'.sel().onclick = () => {
    alert('ok')
}

console.log(String.prototype);

<button btnSend>Send</button>