Sorry, but you can't print that page and use that forever. I understand that you wish that you could, but you can't. I live in the real world, so rather than reading a snapshot and hoping it stays that way forever, I just read the up-to-date version since that's what is implemented by browsers, not the PDF I saved 3 months ago.
Given that the browsers with respect to which you implement the code change under your feet every 6 weeks, I think it's better the standard keeps pace with them than having it give a misleading impression of what you're developing against.
Do you really want to make a requirements document that describes something different at the day you sign it and at the day you deliver?