Why does the :empty pseudo-selector affect elements that don't have a closing tag?

CSS: *:empty { border:green 3px solid; }

1. Image tag: <img src="http://lorempixel.com/400/200/sports/2 " alt="">

   

2. Input: <input type="text">

3. Horizontal Rule: <hr>

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4. Per @davidelrizzo comment, unclosed <p> : It doesn't get affected

5. Here's a short screencast by Russ Weakley in Sitepoint that explains the :empty pseudo-class better:

   Understanding the :empty Pseudo-Class (Screencast)

Created by Ricardo Zea