title: How to make <input type="file"/> accept only these types?
body: <p>I want my uploader only allows these types:</p>
  
  <ul>
  <li>doc, docx.</li>
  <li>xls, xlsx.</li>
  <li>ppt, pptx.</li>
  <li>txt.</li>
  <li>pdf.</li>
  <li>Image types.</li>
  </ul>
  
  <p>How can I achieve this? What should I put in the <code>accept</code> attribute? Thanks for your help.</p>
  
  <p><strong>EDIT!!!</strong></p>
  
  <p>I have one more thing to ask. When the popup appears for use to choose file, at the down right corner, there is a drop down list contains all allow files. In my case, the list would be long. I see in the list, there is an option called <code>All Supported Types</code>. How can I make it chosen by default and eliminate all other options?</p>
  
  <p>Any help will be appreciated. Thank you.</p>