How to get all Errors from ASP.Net MVC modelState?

I want to get all the error messages out of the modelState without knowing the key values. Looping through to grab all the error messages that the ModelState contains.

How can I do this?

foreach (ModelState modelState in ViewData.ModelState.Values) {
    foreach (ModelError error in modelState.Errors) {
        DoSomethingWith(error);
    }
}

See also How do I get the collection of Model State Errors in ASP.NET MVC?.