This is mainly a question about semantic markup. I believe there are some tags which ought to only occur once in an HTML5 document for that document to be considered semantically correct. I believe <nav> is one such tag. I wonder if <h1> also falls into this category. Are there any others? So far this is the list, maybe someone could flush out the list?
<nav><h1>The only tags that need to be unique on the page are:
<html><head>
<title><body>
<main>The rest can occur as many times as you want, and it'll still be completely valid, even semantically.