Add lang= to Jacket?

Is it allowable to add a lang= bit to the HTML line of the jacket in the Editor? Unless it's just a function of something I've done, that line in the current book I'm editing is:
I'd like to add the language stuff so it looks something like:
And, while I'm asking, what about the xmlns:epub= bit? IOW:
Can I, should I, manually change that? Is there a setting in Calibre to do that in the conversion/polish process?