What does this Proxy 'has' trap change about the `in` operator and with-style lookups?
const target = { a: 1 };
const p = new Proxy(target, {
has(t, key) {
if (key.startsWith('_')) return false;
return key in t;
}
});
console.log('a' in p);
console.log('_a' in p);
target._a = 5;
console.log('_a' in p);