document.write.__proto__.toString.toString() BEFORE & AFTER Proxy

console.log("[A]",document.write.__proto__.toString.toString());

// このProxyで、関数名が toString から消える。
document.write.__proto__.toString=new Proxy(document.write.__proto__.toString,{});

console.log("[B]",document.write.__proto__.toString.toString());

(See console for the results...)

document.write.__proto__.toString is a sort of `magic number`.
This happens when it ends with two consecutive toString like "...toString.toString()"
This trick is being used in HObfus.inc.php like

if(!$_isnative("toString",Object.getPrototypeOf($_document.write).toString)){

Is there any other `magic number` that changes the output depending on
the presence of a Proxy?