triggering standards mode first. Which have their own quirks and bugs and stupid design flaws. I do not find the standards are any kind of panacea.
However, it's been some years since I tried <doctype>, since the last time I did, it was disaster. So I don't argue against trying it again. When we are moved to texi2html, I expect we can easily have several output modes, one with the 4.01/transitional doctype, one without, etc. Then people can try and we can gather some actual experience.
