Programming Tips - Why do I get "Stray end tag 'head'" when I do view source in Firefox?

Date: 2016nov8 Product: Firefox Language: html Q. Why do I get "Stray end tag 'head'" when I do view source in Firefox? A. I got this when I accidentally put an <h1> inside a <head>. Since h1 is a body thing it implicitly closed the head and opened the body. So the later explicit end head was called stray. ie:
<head> ... <h1>My Heading<h1> WRONG </head> <body> ... </body>
<head> ... </head> <body> <h1>My Heading<h1> CORRECT ... </body>