title: meaning of "this.el" in $('ul', this.el)
body: <p>I am just going through some backbone tutorials and I have a general jQuery question that I have actually been wondering for a while.</p>
  
  <p>Sometimes I see calls with a second parameter in the jQuery selector, for example <code>$('ul', this.el)</code>.</p>
  
  <p>What is the purpose of this second param in the selector? And I don't really mean in context of any backbone examples, just in general what is the purpose of passing the second param in the selector and why is it always an object that is passed there? I can't find any documentation on this.</p>