[DiapDealer]

I'll try to put together a quick epub as an example.

OK:

Make sure to have all cleaning turned off upon opening/saving and see how the code renders in Book View.

Then change Sigil to automatically Pretty Print the same ePub upon opening it and note how it renders.

I don't know if it has any adverse effect in ADE or other readers, but that attribute can sure create funky results within Sigil's Book View (not that anyone should trust Book View, of course, but I've seen it trip people up before).