Some inline html tags, such as <span> or <a>, have limited functionality in reading view. In general, what it’s written in the docs is correct.
We don’t support markdown with html blocks.
HTML blocks need to be self-contained and without blanks lines in them.
This limitation is an intentional design choice and is due to keeping parsers complexity low (both the editor and reding mode) and a performance optimizations that we use to be able to manage large documents.