docs: public static StringBuilder buildAstString(ParentSoyNode<?> node, int indent, StringBuilder sb) {
      for (SoyNode child : node.getChildren()) {
        sb.append(Strings.repeat("  ", indent)).append(child.getKind()).append('\n');
        if (child instanceof ParentSoyNode) {
          buildAstString((ParentSoyNode<?>) child, indent + 1, sb);
        }
      }
      return sb;
    }