code: public void set(String name, Object obj) throws IOException {
          if (name.equalsIgnoreCase(PERMITTED_SUBTREES)) {
              if (!(obj instanceof GeneralSubtrees)) {
                  throw new IOException("Attribute value should be"
                                      + " of type GeneralSubtrees.");
              }
              permitted = (GeneralSubtrees)obj;
          } else if (name.equalsIgnoreCase(EXCLUDED_SUBTREES)) {
              if (!(obj instanceof GeneralSubtrees)) {
                  throw new IOException("Attribute value should be "
                                      + "of type GeneralSubtrees.");
              }
              excluded = (GeneralSubtrees)obj;
          } else {
            throw new IOException("Attribute name not recognized by " +
                          "CertAttrSet:NameConstraintsExtension.");
          }
          encodeThis();
      }
docs: Set the attribute value.