I like to use a capital H for the breed Harlequin, and a lower-case h for the harlequin pattern, to help clear up confusion.
The Harlequin breed standard gives very clear descriptions of the desired markings, including lots of drawings to supplement the photo since there hasn't really been a perfect Harlequin yet! They are making progress, though. Here's a really interesting article about the breed development:
http://americanharlequinrabbitclub.weebly.com/history---from-the-beginning.html
Brindle actually refers to a distinct pattern, different from harlequin, but which also results from the harlequin alelle
e(j). There is a COD (Certificate of Development) out to add brindle to the Mini Rex breed standard. It specifically disqualifies animals for any identifiable harlequin markings (meaning a large and distinctly solid colored bar or band across the body, or distinct color alternation across the ears, face, chest, or legs). You can see the working standard here:
https://arba.net/wp-content/uploads/2023/06/BrindleMiniRex.pdf
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