<ol>X</ol> is bad HTML

```
<html>
<head>
  <meta name="generator" content=
  "HTML Tidy for HTML5 for Linux version 5.6.0">
  <meta charset="utf-8">
  <title>test</title>
</head>
<body>
  <ol>
    X
  </ol>
</body>
</html>
```
is bad HTML.
See also https://bugs.chromium.org/p/chromium/issues/detail?id=1200889