What is the difference between "data-role" and "role" in the following example ?

What is the difference between "data-role" and "role" in the following example ?

http://api.jquerymobile.com/page/

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   <!doctype html>
  

 

 

  

   <html lang="en">
  

 

 

  

   <head>
  

 

 

  

    <meta charset="utf-8">
  

 

 

  

    <meta name="viewport" content="width=device-width, initial-scale=1">
  

 

 

  

    <title>page demo</title>
  

 

 

  

    <link rel="stylesheet" href="//code.jquery.com/mobile/1.4.5/jquery.mobile-1.4.5.min.css">
  

 

 

  

    <script src="//code.jquery.com/jquery-1.10.2.min.js"></script>
  

 

 

  

    <script src="//code.jquery.com/mobile/1.4.5/jquery.mobile-1.4.5.min.js"></script>
  

 

 

  

   </head>
  

 

 

  

   <body>
  

 

 

  

    
  

 

 

  

   <div data-role="page" id="page1">
  

 

 

  

    <div data-role="header">
  

 

 

  

    <h1>Page header (optional): Example page</h1>
  

 

 

  

    </div>
  

 

 

  

    <div role="main" class="ui-content">
  

 

 

  

    <h2>Page content</h2>
  

 

 

  

    <p>Page content goes here.</p>
  

 

 

  

    </div>
  

 

 

  

    <div data-role="footer">
  

 

 

  

    <h1>Page footer (optional)</h1>
  

 

 

  

    </div>
  

 

 

  

   </div>
  

 

 

  

    
  

 

 

  

   </body>
  

 

 

  

   </html>