As whitespace helps in commenting but whitespace is meaningfull in wikitext, I would create a seperate tiddler where I reformat and describe the text. So no inline comments in the macro.
OTOH - as this is at least double effort - you could try what happens if you insert comments containing linebreaks. like <!-- this is a comment -->so -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/tiddlywiki. For more options, visit https://groups.google.com/d/optout.

