`Symbol.for('x')` and `Symbol('x')` are compared. What is the actual storage mechanism behind `Symbol.for`, and how does it differ from a description-only symbol?
const a = Symbol.for('app.id');
const b = Symbol.for('app.id');
const c = Symbol('app.id');
const r = [a === b, a === c, Symbol.keyFor(a), Symbol.keyFor(c)];