Not wrong, perhaps a little weird. HTML is a first class citizen in the commonmark (spec)[https://spec.commonmark.org/0.31.2/#html-blocks].

"Wrong" does not necessarily mean "against the standard". It means "against common usage and good team practice" in this context.

It's "allowed" to use raw pointers, malloc, and any number of things in C++ code. In general, if you do any of them in a modern codebase you're doing it wrong.