code: private static boolean maybeInitMetaDataFromHelpVar(Builder builder,
        @Nullable Node sibling) throws MalformedException {
      if ((sibling != null) && (sibling.isVar())) {
        Node nameNode = sibling.getFirstChild();
        String name = nameNode.getString();
        if (name.equals(builder.getKey() + DESC_SUFFIX)) {
          Node valueNode = nameNode.getFirstChild();
          String desc = extractStringFromStringExprNode(valueNode);
          if (desc.startsWith(HIDDEN_DESC_PREFIX)) {
            builder.setDesc(desc.substring(HIDDEN_DESC_PREFIX.length()).trim());
            builder.setIsHidden(true);
          } else {
            builder.setDesc(desc);
          }
          return true;
        }
      }
      return false;
    }
docs: Initializes the meta data in a JsMessage by examining a node just before or
  after a message VAR node.
  
  @param builder the message builder whose meta data will be initialized
  @param sibling a node adjacent to the message VAR node
  @return true iff message has corresponding description variable