title: model.frame, UseMethod, and R bytecode reference -- what is this?
body: <p>General context:  I'm trying to find the code that dictates how the model.frame command in R recognizes the class of its argument and subsequently calls one of the model.frame methods.</p>
  
  <p>When I run "model.frame" to reveal its R source code, I get the following:</p>
  
  <pre><code>&gt; model.frame
  function (formula, ...) 
  UseMethod("model.frame")
  &lt;bytecode: 0x21a04c8&gt;
  &lt;environment: namespace:stats&gt;
  </code></pre>
  
  <p>Specific question:  What is "bytecode: 0x21a04c8" telling me?  Is it potentially useful in my context? </p>