code: public static ShadowDocument getOrCreateHiddenDocument() throws FrameworkException {
  
  		final App app = StructrApp.getInstance();
  
  		try (final Tx tx = app.tx()) {
  
  			ShadowDocument doc = app.nodeQuery(ShadowDocument.class).includeHidden().getFirst();
  			if (doc == null) {
  
  				final PropertyMap properties = new PropertyMap();
  				properties.put(AbstractNode.type, ShadowDocument.class.getSimpleName());
  				properties.put(AbstractNode.name, "__ShadowDocument__");
  				properties.put(AbstractNode.hidden, true);
  				properties.put(AbstractNode.visibleToAuthenticatedUsers, true);
  
  				doc = app.create(ShadowDocument.class, properties);
  			}
  
  			tx.success();
  
  			return doc;
  
  		} catch (FrameworkException fex) {
  			logger.warn("Unable to create container for shared components: {}", fex.getMessage());
  		}
  
  		return null;
  	}
docs: Search for a hidden page named __ShadowDocument__ of type.
  
  If found, return it, if not, create it.
  The shadow page is the DOM document all reusable components are connected to.
  It is necessary to comply with DOM standards.
  
  @return shadow document
  @throws FrameworkException