The html-ish pass feeds markdown to htmlparser2 so it can render
<details>, <img> and friends. htmlparser2 reads any `<` followed by a
letter as a tag and collects attributes up to the next `>`. A cell such
as `1<ratio<2` in a table therefore swallowed the rows after it, and the
re-serialized "tag" dropped the newlines and pipes that made them rows.
The same path broke autolinks (`<https://x/y>` became `<https: x y>`)
and cut text after a trailing `a<b`.
Only hand htmlparser2 what CommonMark reads as raw HTML: open tags,
closing tags and comments. Every other `<` stays text.
Unknown tags are rendered back as text, but they were rebuilt from the
parser's lowercased name and attributes, so `As<Integer>()` showed as
`As<integer>()`. Echo the source slice instead.
Jiawen Geng
e2fd5a9c57