Function body_entity 

pub fn body_entity(body: &str, flowed: bool, markdown: bool) -> String

The draft’s text as a MIME entity: text/plain, or with markdown compose a multipart/alternative of that text/plain and the text/html rendered from it. The plain half comes first, so a reader that shows the last part it can (every graphical one) shows the html, and a plain one loses nothing.