We restrict the resources that user-created webpages can bring in for security and moderation reasons. Specifically:
- Webpages can bring in images from Khan Academy static servers, and Wikipedia. The webpages should attribute images properly, like using CC licenses for Wikipedia images.
- Webpages can bring in CSS and font files from Google Web Fonts and Twitter Bootstrap.
- Webpages can bring in sounds/videos from Khan Academy static servers.
The resources must all come in over SSL, so the URLs should start with https://. Remember to check your developer console for errors if you're having trouble bringing in any of those resources.