title: Hidden features of HTML
body: <p>HTML being the most widely used language (at least as a markup language) has not gotten its due credit. <br/>
  Considering that it has been around for so many years, things like the FORM / INPUT controls have still remained same with no new controls added.</p>
  
  <p>So at least from the existing features, do you know any features that are <strong>not well known</strong> but very useful.</p>
  
  <p>Of course, this question is along the lines of:</p>
  
  <p><a href="https://stackoverflow.com/questions/61088">Hidden Features of JavaScript</a><br />
  <a href="https://stackoverflow.com/questions/628407">Hidden Features of CSS</a><br/>
  <a href="https://stackoverflow.com/questions/9033">Hidden Features of C#</a><br />
  <a href="https://stackoverflow.com/questions/102084">Hidden Features of VB.NET</a><br />
  <a href="https://stackoverflow.com/questions/15496">Hidden Features of Java</a><br />
  <a href="https://stackoverflow.com/questions/2963484">Hidden Features of classic ASP</a><br />
  <a href="https://stackoverflow.com/questions/54929">Hidden Features of ASP.NET</a><br />
  <a href="https://stackoverflow.com/questions/101268">Hidden Features of Python</a><br />
  <a href="https://stackoverflow.com/questions/605439">Hidden Features of TextPad</a><br/>
  <a href="https://stackoverflow.com/questions/54886">Hidden Features of Eclipse</a></p>
  
  <p>Do not mention features of HTML 5.0, since it is in <a href="https://stackoverflow.com/questions/605439">working draft</a><br/></p>
  
  <p><strong>Please specify one feature per answer</strong>.<br/></p>