I was going through the source code of jQuery. I'm having trouble understanding the wrapping strategy for the jQuery object.

(function( window, undefined ) {

    // Define a local copy of jQuery
    var jQuery = function( selector, context ) {
            // The jQuery object is actually just the init constructor 'enhanced'
            return new jQuery.fn.init( selector, context );
        },

    ....
    ....
    ....

    // Expose jQuery to the global object
    window.jQuery = window.$ = jQuery;

})(window);

Specifically, what I'm not able to understand stems from the first line.

1. What is the outermost unnamed container function? Why is it required?

2. Why is the container function anonymous?

3. What is the need for the outermost '(' parantheses ?