MVC4 [AllowHtml] DataAnnotation not recognized?

Question

I have an existing class in an MVC4 project (also using EF 4) that I need to set for the [AllowHtml] DataAnnotation parameter. I already have annotations on several properties of this class (i.e. Mandatory display), which work fine. The corresponding libraries are included:

using System.ComponentModel.DataAnnotations; using System.ComponentModel.DataAnnotations.Schema; 

However, an error message appears:

Unable to resolve symbol [AllowHtml]

Here is the code. The first two annotations work. Third, no. I tried to install it separately from others, which did not matter. What am I missing?

 [Display(Name = "Title"), Required, AllowHtml] public string Title { get; set; } 

Answer 1

AllowHtml is in the System.Web.Mvc namespace

http://msdn.microsoft.com/en-us/library/system.web.mvc.allowhtmlattribute(v=vs.98).aspx