I wonder if it's worthwhile having that line in there. I'd be willing to
bet there are a lot of people who think the default format is just fine but
don't particularly like that line. Those people now have to learn about the
mhl command, figure out the right place to copy the file to, etc. And I
don't think it's a particular help to mhl experts, either...
I have a thing against unnecessarily chatty software. Why not make the
default be something that's attractive and usable without tweaking
(mhl.format _is_, except for that line).
I've changed the line " -- using template mhl.format -- " to a blank
line in the default mhl.format. I agree that it is unnecessary clutter.