title: Restrict upload to file extensions in jQuery Validation
body: <p>I want to perform validation with the jQuery Validation plugin for <code>input</code> <code>type="file"</code>.  I want to restrict file formats to <code>doc,pdf,rtf, and docx</code>.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>  $("#contact-form").validate({ 
            onfocusout: function(e) {
                this.element(e);
              },
          rules:{
  
              resume:{
                  required:true,
                  extension: "docx|rtf|doc|pdf"
              }
  
          },
      resume:{
                  required:"input type is required",                  
                  extension:"select valied input file format"
              }
  
  
      });
  </code></pre>