{"ast_node_type":"variable","tokens":[{"end":95,"kind":"keyword","start":0,"text":"let"}]}
    let (t, r) = parse_simple_pat(buf.as_bytes(), CMT_S, CMT_E, opt, MdTree::Comment).unwrap();
    let buf = "<!-- foobar! -->rest";
    assert_eq!(t, MdTree::Comment("foobar!"));