code: public com.sun.javadoc.Type containingType() {
          if (type.getEnclosingType().hasTag(CLASS)) {
              // This is the type of an inner class.
              return TypeMaker.getType(env, type.getEnclosingType());
          }
          ClassSymbol enclosing = type.tsym.owner.enclClass();
          if (enclosing != null) {
              // Nested but not inner.  Return the ClassDoc of the enclosing
              // class or interface.
              // See java.lang.reflect.ParameterizedType.getOwnerType().
              return env.getClassDoc(enclosing);
          }
          return null;
      }
docs: Return the type that contains this type as a member.
  Return null is this is a top-level type.