Everything you do is written into the file itself as plain text, so anyone can see it in any editor. Five marks are standard CriticMarkup; the last two are this tool's own.
{++ … ++}{-- … --}{~~ old ~> new ~~}{>> … <<}{== … ==}{>> … <<}{!! … !!}This tool{@@ who time sha256 @@}This toolPress E or click into a passage and edit it as ordinary text. When you save, your version is compared with the original words and the additions, deletions and substitutions are written for you. Edit the same passage again and the marks are rewritten against the original, so they never pile up; put a word back and its mark disappears.
To comment, select some words in the editor and press Comment: they are highlighted and your note is attached. With nothing selected, the comment goes at the cursor.
Plain markdown is the text as it now reads: additions and substitutions applied, deleted and removed text gone, comments and every other mark dropped. With ownership marks keeps every mark, so a colleague can see what changed, what was skipped and who owns it.