Is it invalid/confusing to have a <header> in the middle of a document
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I currently have a setup like this:

    <section id="intro"></section>
    <header></header>
    <section></section>
    <section></section>
    <footer></footer>

The header element is a sticky header with site name and basic information. It doesn't show until after the user scrolls past #intro, hence where it is in the DOM. I was wondering if, from the point of view of semantics and accessibility, it made more sense to just make it a div or a section.