txt derivative files are to be provided as raw-ish data for others to analyze as textual information.
What tags need to be signified? These should only be things that the author himself has on the page and characterizes as different types of info. How should they be rendered (as the only allowable rendering is by insertion of special characters)?
DECISION: The only tags to be included are del render them in txt as follows: <del></del> becomes <--> e.g., <del>word</del> becomes <-word->