<a href="//example.com" target="_blank">Example</a>

Have you ever seen a link like the one above and wondered what they are all about, well let me take you on a magical journey...

Normally you see links prepended with http:// or https:// but // actually means simply means the browser will grab which ever is available.

How does this work?

It does this by trying to access the content via http and https and using which ever works, favoring https when it is available.

The downside to this means the content is downloaded twice in some cases.