title: Simple about jquery source,confusing about "this" keyword
body: <p>I felt very confused about "this" keyword in jquery 1.7.3 source.some snippets showing below: </p>
  
  <pre><code>jQuery.fn = jQuery.prototype = {
  constructor: jQuery,
  init: function( selector, context, rootjQuery ) {
      var match, elem, ret, doc;
  
      // Handle $(""), $(null), or $(undefined)
      if ( !selector ) {
          return this;   
      }
  
      // Handle $(DOMElement)
      if ( selector.nodeType ) {
          this.context = this[0] = selector;
          this.length = 1;
          return this;
      }
  </code></pre>
  
  <hr>
  
  <pre><code>if ( !selector ) {
  
    return this;   //why not only one "return" here?
                   //And does "this" refer to jQuery object?
                   //OTOH, this question is about why it returns "this".
  }
  </code></pre>