pageoneresults - 3:55 pm on Jun 30, 2010 (gmt 0)
"Content is "equivalent" to other content when both fulfill essentially the same function or purpose upon presentation to the user."
The above quote comes from the WCAG (Web Content Accessibility Guidelines) and refers to attributes that are utilized to present alternative content, the alt attribute being one of those.
The title attribute is an advisory element. It is typically invoked on hover and provides advisory information. I use them quite a bit on table headings in tight confined areas where we have to use brevity in visual text.
I believe that all content that is left after stripping markup is utilized to some degree. Content that resides in title attributes would be part of that. But, it's not to be used for what some might think. If you replicate in the title attribute that which surrounds it textually, I think it just negates itself. You also bring in the stuttering effect. My understanding is that certain software for accessibility allows the user to listen to advisory attributes, the title being one of them.
WordPress realized their users were stuttering out of the box and they have a Plugin to stop the madness! ;)
Remove Title Attributes
When it comes to the alt attribute and images, we've had some very lengthy discussions on that. I typically refer back to this one started by phranque...
Accessibility and <h1> Header Images
From the above discussion, I produced a document to show proof of concept. phranque makes me dig deep into the bowels of the W3 to find the really good stuff. :)
Image Replacement Technique