title: How to tell if a browser is in "quirks" mode?
body: <p>Let's suppose you have a page with a relatively strict doctype and HTML markup that's pretty close to compliant, but perhaps misses in a few silly ways, perhaps because of user content that's out of your control... say you're working on a content management system or a theme for a content management system where you control some basic structure and need some javascript, but you're not responsible for everything else that goes into pages.</p>
  
  <p>How can you tell (or: what will determine) when the browser decides to go into "quirks" mode rather than use it's more standards compliant engine?  </p>
  
  <p>I'm looking for answers for each of the major browsers, since IE, Chrome, Safari, and Firefox will of course all handle that differently.  Is one single error enough to force it or do you have some leeway?</p>