The Tangled Web

Chapter 13. Content Recognition Mechanisms

So far, we have looked at a fair number of well-intentioned browser features that, as the technology matured, proved to be short-sighted and outright dangerous. But now, brace for something special: In the history of the Web, nothing has proven to be as misguided as content sniffing.

The original premise behind content sniffing was simple: Browser vendors assumed that in some cases, it would be appropriate—even desirable—to ignore the normally authoritative metadata received from the server, such as the Content-Type header. Instead of honoring the developer’s declared intent, implementations that support content sniffing may attempt to second-guess the appropriate course of action by applying proprietary ...