I mentioned that it has no IE or Edge support, and that I was perfectly OK with that. So… why did I decide it’s perfectly fine to not support a feature for a major browser?
For me, the line is access to content.
summary feature isn’t supported by a browser, users get… all of the content. The toggle is shown, the content is shown, and nothing ever gets hidden.
To me, the expand/collapse functionality is a progressive enhancement. Great for users that support it, but an extra nicety that browsers that don’t can comfortably go without.
If that content was hidden and inaccessible on unsupported browsers, I would feel differently.