title: Does .toString(16) always return lowercase?
body: <p>When converting a decimal number to a base above 10 using <code>.toString(base)</code>, it seems that I always get a lower case string. <strong>Can I rely on this</strong>? An upper case string would be correct, although would need converting for my application.</p>
  
  <p>Extra credit for referencing the part of the spec that defines this (I looked and couldn't find it) and for any counter-examples (browsers that return uppercase).</p>
  
  <p>Example:</p>
  
  <pre><code>(12648430).toString(16) // returns: "c0ffee". Not "C0FFEE"
  </code></pre>