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The new <command> will not validate html5. Using this as an example http://www.w3schools.com/html5/tag_command.asp error: Stray end tag command.
The command element is a void element (like the img element), so it's not allowed to have an end tag. By the way, I suggest you don't w3schools as a source for information about HTML5. There are many errors in their content, and they don't fix the errors even after users report them. For correct reference information on the command element, try http://dev.w3.org/html5/spec-author-view/interactive-elements.html#the-command or http://dev.w3.org/html5/markup/command.html or
Why it not recognize end of img tag? With "/>" and just ">". Validator says one. And... Down in the document, and in other documents recognize... What is this? Line 73, Column 208: Stray end tag img.