Hi Greg,
I recently decided to check whether our library's website was using valid HTML pages, and what I found wasn't very pretty. If you haven't already checked, you can see the results for yourself here:
http://validator.w3.org/check?uri=http%3A%2F%2Frhpl.richmondhill.on.ca%2F&charset=%28detect+automatically%29&doctype=Inline
I don't know whether you know this already or not, but having valid webpages is very important especially for a public library website. In any case, I'll point you to what the W3C team has to say about this:
http://validator.w3.org/docs/help.html#why-validate
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