title: System.Web.Mvc missing reference to ModelClientValidationRule
body: <p>I am trying to write some client validation in a class library. I added a reference to System.Web.Mvc on my local machine here <code>C:\Program Files (x86)\Microsoft ASP.NET\ASP.NET MVC 4\Assemblies\System.Web.Mvc.dll</code> but I am getting the error </p>
  
  <blockquote>
    <p>The type or namespace ModelClientValidationRule could not be found
    (are you missing a using directive or an assembly reference?)</p>
  </blockquote>
  
  <p>I am targeting .Net Framework 4 and <a href="https://msdn.microsoft.com/en-us/library/system.web.mvc.modelclientvalidationrule(v=vs.100).aspx" rel="nofollow">this MSDN link</a> indicates that should be correct, so I am little stumped as the why the error is occurring.</p>
  
  <p>I am using VS2013 and have .Net 4.5 on my local machine, and have written client validation in other projects. I expect that I could resolve this issue by adding the MVC NuGet package, but I would like to explore the alternatives.</p>