victor - 12:53 pm on Feb 21, 2006 (gmt 0)

If your HTML and CSS do not vaildate, then you may need to test the site in every possible user agent to ensure that the bugs in the code do not cause the user agent to trip up in some way.

That's not just an accessibility issue: any bug needs to be tested to ensure in has no unseen consequences.

If you stick closely to exactly the bugs in the HTML and CSS of some popular sites (like Google or Yahoo) then you have some degreee of confidence that those bugs are benign across the range of user agents that [eg Google / Yahoo] consider their market.

If you insert other untesed bugs, then the onus is on you to roll out a testing program.