code: protected boolean isPage(PRIndirectReference ref) {
          IntHashtable refs = (IntHashtable)pages2intrefs.get(ref.getReader());
          if (refs != null)
          	return refs.containsKey(ref.getNumber());
          else
          	return false;
      }
docs: Checks if a reference refers to a page object.
  @param	ref	the reference that needs to be checked
  @return	true is the reference refers to a page object.