thead > td is not formatted as a header

Created by: andrewnicols

Prerequisites

• I have searched for duplicate or closed issues
• I have validated any HTML to avoid common problems
• I have read the contributing guidelines

Describe the issue

The thead tag should cause all child content to be treated as a header, however if you write a table with a <td> within the <thead> tag, it is treated differently to a <th> tag.

This topic is discussed within the W3C HTML specification in this issue where it is declared that any content of a thead should be treated as a header. The wording of the specification is amended to:

The thead element represents the block of rows that consist of the column labels (headers) for the parent table element, if the thead element has a parent and it is a table.

https://html.spec.whatwg.org/#the-thead-element

The apparent intent (from the bug above) is that all content of a <thead> tag should act as, and appear as, a header.

At present this is not the behaviour and a thead > td appears differently to a thead > th.

Reduced test cases

https://codepen.io/andrewnicols/pen/vYrvXBX

What operating system(s) are you seeing the problem on?

macOS

What browser(s) are you seeing the problem on?

Chrome, Safari, Firefox, Microsoft Edge

What version of Bootstrap are you using?

4.6.0; 5.2.x