We use a fat layer navigation which partly consists of content that some CMS users insert with a rich text editor (TYPO3 is the CMS btw).By this we have several <hX> tags inside the <nav> tag which contains the navigational layer.Now a SEO agency tells us that this is bad. I searched the internet and the few answer I got are contradictory.Are there any facts that say bad or not?The real code is not insteresting from my POV. But here is an abbreviated example: jsfiddle.net/5Ldjvytr 
Several headings inside 
seo;html5