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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
I had the same message because I used double quotes instead of single quotes (as expected) inside the A element.
I understand that the author is not going to write or instanciate an HTML parser to check the answer against all different ways of writing an A element, but a helpful error message or a tip is in order here, if no other change is reasonable. It is an issue.