title: Assembly and Namespace for NUnit's Constraints Model
body: <p>I want to use the new <a href="http://nunit.com/index.php?p=constraintModel&amp;r=2.4.8" rel="nofollow noreferrer">Constraint-based model</a> in NUnit. In which assembly and namespace are the classes defined? (Specificially, I'm looking for the "Is" class and the IConstraint implementations discussed in the documentaton). They do not seem to be in NUnit.Framework.</p>
  
  <p>Also, I'm interested in v2.4.8, which as of this writing is the latest stable release.</p>