title: How do I set the default application for xdg-open on a callto: or skype: URL?
body: <p>I'm writing a Chrome extension which links phone numbers in the page so you can click them and make a Skype call. </p>
  
  <p>Chrome on Linux uses <code>xdg-open</code> to delegate external URL handling, and it doesn't understand <code>callto:</code> or <code>skype:</code> URLs. I know that if I can figure out the appropriate mime-type I can use <code>xdg-mime default</code> to set Skype as the handler, but I've searched and can't find anything on the topic. </p>
  
  <p>How can I set this up so that <code>xdg-open callto:+1234567890</code>, for instance, will place a call using Skype?</p>