I don’t like displayHtml. I’m new here and maybe I don’t get something! But it seems to me that certificates should provide data only, and let the end-user frontends do what they want with it.
There’s also the fact that there’s only a PR now to include displayHtml in cert-tools. Moreover, the HTML can evolve over time, we can never know if in a few years the display will still be valid.
It’s also a pitty that BlockCerts mobile app requires this. IMHO, it should display displayHtml when it’s there, and provide a standard display otherwise.
That’s just my opinion anyway, and I would be curious to know yours.
Best,
Guillaume
I don’t think we like it much either 
I’ll try to communicate what I’ve picked up about displayHtml, although it might not be 100% complete, so other blockcerts members can correct me or put in their 2 cents.
There’s trade offs and pros and cons to it. Providing certificates that look the same across all devices, browsers, and apps is a hard thing to accomplish, while keeping the integrity and verifying that the way it looks to a verifier is the way that the issuer designed it. For certificates that are typically physical and visual, there’s value in providing the same visual experience in digital form here as well. Graduation records and the designs that go into them are the big ones that come to mind.
I think the reason it’s not in cert-tools right now is because we didn’t want it to be part of the standard, at this time. It’s a weird situation, especially since we currently rely heavily on displayHtml. I think we do want to improve this, and there’s talk in the verifiable credentials community on how to handle verifiable displays.
IMHO, it should display displayHtml when it’s there, and provide a standard display otherwise.
I agree. In fact, when a couple of us talked about it today, we thought it did provide a default view. Since we mostly deal with certs that have displayHtml, it’s not something that we test or run into all that much.
Have you experienced what happens when you try to import a cert that does not have displayHtml?
Thank you Anthony for this detailed explanation 
I now see how this is a complex topic. Well, we will see how it evolves…
A cert that has no displayHtml can be retrieved in the Android App, and is correctly listed in the certificate’s issuer screen, but not when displaying the certificate in itself. You can try for instance with https://raw.githubusercontent.com/blockchain-certificates/cert-verifier-js/master/tests/data/sample_cert-valid-2.0.json