I have the following piece of HTML that creates a new window when clicked:
glide by the people
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If you have a requirement for Accessibility or Cross-Platform Interoperability, you likely want to validate your web page. There is a nice document answering the question about "why validate?" posted by W3.org http://validator.w3.org/docs/why.html
IMHO, it shows you care about your audience, when you take the extra time to validate. Then, you will have pages that show virtually the same on IE, Opera, Safari, and Firefox.