title: What is the isa instance variable all about?
body: <p>In the NSObject Class Reference they talk about an "isa instance variable" which </p>
  
  <blockquote>
    <p>is initialized to a data structure that describes the class</p>
  </blockquote>
  
  <p>can someone explain what I should know about this isa instance variable? What is that good for? What does isa mean? Sounds like a norm, like DIN, ISO, etc.; Any idea what that is?</p>