Thanks John, you asked about the Medium bookmarklet. Yes of course, you can use Write in Medium as a browser add on (a bookmarklet); I am now writing from a mobile device on the run, later I shall add the link. The way I use it is to highlight a passage in Medium and click on the write in medium bookmarklet. It brings me to medium and I can continue to finish writing.
Another way you can do this is to highlight a passage and then copy and paste into the comments section and this becomes both a comment and a new post.
Speaking about lack of a “manual” of medium, I agree with you. I wrote a “cheat sheet” for medium sometime ago, I shall upload the link once I return to my desktop. See if this will be helpful for you.