May I remind you all that the Validator is a mark-up validator, not just
HTML, so it must be able to handle other FPIs, I.e. by using the SI -
viz. it should yes throw a warning when the FPI and SI do not match the
specification, but when it doesn't know at all what the FPI stands for
it should use the SI.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
would throw a warning only(although a SI override I.e. use SI not FPI
would be nice)