Function xml_ref_attr 

pub fn xml_ref_attr<T: ReadTxn, N: Xml>(
    txn: &T,
    node: &N,
    name: &str,
) -> Option<String>

An attribute reference on a node: rules say :kind; Lexical stores its own props as __kind — try the raw name first, then prefixed. (ProseMirror stores attrs bare, so the fallback never fires there.)