Javascript: what is $$?

Question

I saw this using "$$", for example:

[].forEach.call($$("*"), function(a) { a.style.outline = "1px solid #" + (~~(Math.random() * (1 << 24))).toString(16); 

 function Main() { [].forEach.call($$("*"), function(a) { a.style.outline = "1px solid #" + (~~(Math.random() * (1 << 24))).toString(16); }); //sorry, didn't find credit, but thanks to author } $(document).ready(function() { //Main(); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div>Some Text</div> 

Unfortunately, searching $$ anywhere (google, yahoo, jquery site, jquery file, stackexchange) on the Internet does not return a result.

I see what he is doing, but would like to know where he is from?

And I'm also interested in how I could find the answer myself, because I cannot find it or look in the jQuery API documentation . thanks

Edit:

• This is not a duplicate of JavaScript Double Dollar Sign . I'm talking about the $$ variable, actually bound to something even on a blank page without loading js. Opening a chrome console and typing $$ should allow someone to respond
• (I wonder why the search engine cannot return the result when searching for $$)