Heads up! This blog post hasn't been updated in over 2 years. CodePen is an ever changing place, so if this post references features, you're probably better off checking the docs. Get in touch with support if you have further questions.
This feature now works better than ever. External Resources that are on a non-CodePen URL are linked to in the head properly. Pens as External Resources are also exported and linked to relatively. HTML includes are injected into the final output and noted with comments. License is added automatically, except on Private Pens.
Couple other little fixes too. We created a proper Docs page for it.