- I'd suggest looking into the `doc-notice`, `doc-tip`, and `doc-example` [DPUB-ARIA](https://w3c.github.io/dpub-aria/) roles. I'm a big fan of DPUB-ARIA and I do not think it is used enough. I believe Google's Talkback has the most robust support for it put of any AT I'm familiar with.
- I'm not convinced that a `cot` element is necessary. I think a heading with `aria-labelledby` would work better as a way to name a callout, and an attribute (or DPUB-ARIA role) could better specify the type of callout.
Funnily enough, I'm thinking about my own proposal for a `spoiler` element which also has similar structure to—but different semantics from—the `details` element.