Knockout.js Data-bind Attribute Causes Html Validation Warning

I'm using the HTML Validator firefox add-on and when I go to the home page of http://knockoutjs.com/, I get warnings about the data-bind attribute (for the Live Example): Examples:

Solution 1:

They are HTML 5 custom attributes. Try to validate against HTML 5 specs and you should get an ok on the validation.

But since long you have been able to use custom attributes as you see fit although it may have violated strict HTML 4 specs.