Describe @isolatedParam

Part of #145.

lang/spec.html

@@ -8892,7 +8892,13 @@ <h2 id="lang_library">10. Lang library</h2>
 has a <code>@typeParam</code> annotation, it means that this type serves as a
 type parameter when it is used in a function definition: all uses of the type
 parameter in a function definition refer to the same type; the definition of the
-type is an upper bound on the type parameter.
+type is an upper bound on the type parameter. A parameter of a function
+definition can be annotated with an <code>@isolatedParam</code> annotation; this
+is allowed when the function is declared as isolated and the type of the
+parameter is a function type; the meaning is that when the function is called in
+a context that requires it to be isolated, then the argument supplied for the
+parameter must also be isolated. In effect, the function is parameterized with
+the isolated qualifier.
 </p>
 <p>
 <strong>Note</strong> We plan to provide full support for generic types in