Is this a valid HTML5

[Licedache]

My HTML5 codes goes like this;\[code\] <header id="header"> <div class="container"> <h1></h1> <p></p> <ul class="ico"> <li></li> <li></li> <li></li> </ul> </div></header><section id="about" class="container"> <header> <h1></h1> </header> <nav> <ul> <li></li> <li></li> <li></li> <li></li> </ul> </nav></section> <section id="content"> <article> <div> <p></p> </div> </article> </section>\[/code\]I have a confusion that is it possible to include the nav tag inside a section. Also is it valid to add the div tag inside an article tag. So above mentioned codes are valid in HTML5?