A file called choices.txt that containing pure ASCII (not a word processor format) text describing the significant design choices you made.
So, I will go ahead with providing both choices.txt and choices.html. I hope there won't be an automatic failure.
For the user guide though I have an option of text file or html file.
you must provide either a single plain ASCII (not word processor format) text document, which must be called userguide.txt, or multiple HTML files which must all be accessible from a starting point document that must be called userguide.html.