Comment by honr

No, it's just that I wasn't very clear.

HTML I can view in any browser / webview / etc. Good markdown viewers are fewer / more special, or end up translating md to html for display.

And by composing, I didn't mean writing by hand. We are talking about prompting, right? Or that is what I thought we are talking about. Composing HTML "components" into a final prompt HTML is easier than composing markdown snippets into the final prompt. That is because with HTML there are several ergonomic libraries to parse HTML to AST and to format AST back to HTML. The libraries (for parsing to AST and back to strings) are more limited with markdown.