When I just read "Discussion" section of last v0.37-draft, I spotted typo: "adn" should be "and".And then I remembered that in summer Luke Leighton proposed patch correcting exactly that problem:
Patch for two spotted typos included.Please apply...
The other one wasn't a typo. ZBitfield32 would be a standard extension, XBitfield32 a non-standard extension. So the sentence "Note that we do not propose XBitfield32 as a standard extension. There will never be a ZBitfield32 extension." is correct as it is.