Which DOM elements can be child of tr?

W3C specify this stuff. For tr, you can find it here. Basically, only th and td elements can be direct contents of tr.

If you want other stuff inside your table, it has to go inside the td or th elements. For example, td can contain flow elements, including div.

The HTML spec states:

Permitted contents

Zero or more of: one td element, or one th element

<tr> elements can contain only <td>s and <th>s.