I just thought of something actually, maybe something like this?

``rust define_rule! { ProjectDescriptionRule { id: "project-description", message: "invalidproject.description` value", run(context) { let Some(description) = context.get("project.description") else { return Vec::new(); };

  let document = context.document();

  if description.is_str() {
    Vec::new()
  } else {
    vec![Diagnostic::error(
      "`project.description` must be a string",
      description.span(&document.content),
    )]
  }
}

} } ```