title: how does getElementsByClassName() work under the hood?
body: <p>I've tended to just loop over elements selectively to find elements of a specific class, but I'm curious if using getElementsByClassName (for applicable browsers) will increase performance at all.</p>
  
  <p>How does it actually WORK?</p>
  
  <p>I could easily run a test to check performance obviously, but I'm really curious what's going on in there anyway.</p>