You're absolutely correct that this won't save us from brain-dead engineers, what it will save us from is broken browsers which misinterpret otherwise legitimate data and get broken out of their proper context. (Yes, I've seen browsers do exactly this, and you can probably guess which versions)
Could you explain in which context? I.e. say I had a broken browser, and some JSON data having <foo> inside it - in which context that could get me into trouble?
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Stanislav Malyshev, Zend Software Architect
stas@zend.com http://www.zend.com/
(408)253-8829 MSN: stas@zend.com