W3C Validation says: Elements are undefined
I am making a fixed layout eBook in xhtml, using Dreamweaver. I am trying to mark out a section using html5 tags: <article> and <section>. Everything looks OK, but when I validate it, I get the error message: element "article" undefined [XHTML 1.1]
Is it possible to use these elements with XHTML?
Is there a way to avoid these error messages?
Is it OK to ignore these error messages for ePubs?