error: unclosed HTML tag `unknown`

[StackOverflowExcept1on]

#! ## Panic handler profiles

## When enabled, a minimal panic handler is provided by this crate.
## Instead of a panic message, "<unknown>" is displayed.
panic-handler = ["const_format"]

For some reason I can't write <tag> in doc comment.

[ogoffart]

That's a rustdoc thing. You need to escape it. eg: `<unknown>` or \<unknown>