code: public void set(String name, Object obj) throws IOException {
          if (obj instanceof Extension) {
              map.put(name, (Extension)obj);
          } else {
              throw new IOException("Unknown extension type.");
          }
      }
docs: Set the attribute value.
  @param name the extension name used in the cache.
  @param obj the object to set.
  @exception IOException if the object could not be cached.