Default value for readonly intersection

Fixes #544

lang/spec.html

@@ -2938,6 +2938,14 @@ <h4>Intersection types</h4>
 <code>readonly&amp;T</code>, where <code>T</code> describes the primary aspect
 of the shape.
 </p>
+<p>
+When T is either <code>R&amp;readonly</code> or <code>readonly&amp;R</code>,
+where R is a record type descriptor, and a field in R has a default value with
+closure C, then, if the return type of C belongs to <a
+href="#Cloneable">Cloneable</a>, the field in T has a default value with a
+closure that applies the <a href="#>ImmutableClone</a> operation to result of
+evaluating C; otherwise, the field in T does not have a default value.
+</p>
 </section>
 
 <section>