HTML Attribute rel Errors using fancyBox

Question

I\'m using fancyBox to create a gallery with the following code:

Answer 1

How do I fix this issue?

You don't need to. The range of values that the validator accepts for the rel attribute is limited.

Obviously Fancybox makes use of that attribute in a way that the validator does not appreciate, so it issues a warning an error; but this does not have to concern you.

Am I not writing the code out correctly?

Yes, you are.