“Start tag in table body” message for <thead><th></th></thead> is confusing

see screenshot

![image](https://user-images.githubusercontent.com/280571/103038555-5fa1fe80-4534-11eb-8d0e-58a5bdc825fa.png)



html code:
```html
<!DOCTYPE html>
<html lang="">
<head>
<title>Test</title>
</head>
<body>
<p></p>
<table>
    <thead>
        <th></th>
    </thead>
</table>
</body>
</html>
```
