title: ASP.NET MVC different helpers types
body: <p>I wonder why classes in Microsoft.Web.Helpers.dll such as Facebook, Twitter don't use HtmlHelper? They are still helpers, arn't they?</p>
  
  <p>For some reason they derive from HelperPage. However all their logic resides in static methods.</p>
  
  <p>Can someone explain this to me? If I want to write my own helpers, should I always use extensions over HtmlHelper or do it like in Microsoft.Web.Helpers.dll? What are pros and cons?</p>
  
  <p>Thanks.</p>