[KevinH]

I am confused. That was the point of the requested change for "Mend and Prettify", ie. that it check for well-formed before running it. It forces people to not run that command until after the source is well-formed. So just Mend or hand fixing until well formed, then running Prettify.

"Mend and Prettify" is actually not two different steps. It parses any xhtml using gumbo (whatwg) and the when serializing the DOM tree back to xhtml, it does the prettify part.

The actual name of the command indicates how it works (ie it runs the gumbo repair parser then when serializing it back it does the prettify part. Normally that is safe but as you saw it can cause issues when attributes are not properly quoted, and since Prettify changes whitespace wholesale, it can be a bit disruptive at times.

So Mend vs Mend and Prettify are two different commands that each first parse the xhtml using a repair/whatwg parser then just serialize the DOM tree in different ways. The latter has never been running Mend first then Prettify.