title: Is it OK to use unknown HTML tags?
body: <p>Correct me if I'm mistaken, but AFAIK, unknown HTML tags in markup (i.e. tags not defined in the HTML spec, like say, <code>&lt;foobar&gt;</code>) will eventually be treated as a regular <code>&lt;div&gt;</code> in an HTML 5 browser environment.</p>
  
  <p>I'm thinking: how supportable is this practice? I mean, if I use unknown HTML tags in my markup, what pitfalls can I expect? Will <a href="http://xkcd.com/292/" rel="noreferrer">a velociraptor pounce on me within the next few seconds</a>?</p>
  
  <p>The reason I ask is that if these tags defer to <code>&lt;div&gt;</code>, I can potentially use these tags in a more semantic manner than, say, assigning class names that identify modules. <a href="http://www.stubbornella.org/content/2010/06/25/the-media-object-saves-hundreds-of-lines-of-code/" rel="noreferrer">Have a look at this article, for example, of a <code>.media</code> class</a>. Now what if instead of writing up that CSS to target <code>.media</code>, I make it target <code>&lt;media&gt;</code> instead? In my opinion, that makes the markup much more readable and maintainable, but I do acknowledge that it's not "correct" HTML.</p>
  
  <h3>EDIT</h3>
  
  <p>Just to be transparent, I <em>did</em> find <a href="https://stackoverflow.com/questions/211394/when-to-use-custom-html-tags">this SO question from a few years back</a>. It's been closed as off-topic, but I feel that I have a valid point in my own wording. It's a close duplicate, I admit, but it's from a few years back, so there might have been changes in the general environ of opinions across web developers about the topic.</p>