title: Should you define an abbreviation more than once with the <abbr> tag?
body: <p>If I have an article or blog post and I have an abbreviation or acronym such as SAD (Seasonal Affective Disorder) should I do this <em>everytime</em> the acronym SAD appears in a document?</p>
  
  <pre><code>&lt;abbr title="Seasonal Affective Disorder"&gt;SAD&lt;/abbr&gt;
  </code></pre>
  
  <p>If you do only define it once, does it have to be the very first time the abbreviation appears or could it be the 3rd or 4th time?</p>