title: How to detect Content Security Policy (CSP)
body: <p>I noticed that GitHub and Facebook are both implementing this policy now, which restricts third party scripts from being run within their experience/site.</p>
  
  <p>Is there a way to detect whether a document is running against CSP using <strong>JavaScript</strong>?
  I'm writing a bookmarklet, and want to give the user a message if they're on a site that doesn't support embedding a script tag.</p>