[AlanHK]

Originally Posted by KevinH

And fwiw, that Jutoh "comment" is no longer correct as soon as Sigil open the OPF, cleans and parses it to set up the file. Sigil is the generator of that file from that moment onward.

When Sigil opens imperfect epubs, it tries to repair them.
Consider converting comments in OPFs to something valid that retains the information on opening.
"Cleaning" the OPF doesn't have to mean deleting every imperfect element.

Originally Posted by KevinH

The OPF as with the nav and ncx are truly meant to be machine parseable.

But also human readable and often edited.
I manually remove junk or fix stuff in them all the time.

The "<meta content" I used passes epubcheck, but I don't care what tag it has, the important thing to me is that the information is not lost before I even know it was there.

Originally Posted by KevinH

You can set an environment variable to turn off Sigil adding its own metadata. And the date modified must always be added according to the epub3 spec each time the epub is modified.

I mentioned that not to complain but to point out that every editor uses a different method to do this.
Jutoh unfortunately chose a method that isn't kosher.

I have occasionally noticed other programs putting info in HTML comments in the OPF. Only rarely do I peek at the OPF outside Sigil, so I can't say just how common this is, but it is not just Jutoh.