A DOCTYPE (short for “document type declaration”) informs the validator which version of (X)HTML you’re using, and must appear at the very top of every web page. DOCTYPEs are a key component of compliant web pages: your markup and CSS won’t validate without them.

The DOCTYPE switch stood designers and developers in good stead as a toggle between standards mode and quirks mode. The switch enabled browsers to accurately support the work of responsible designers who cared about accessibility, findability, and lean, semantic markup. It also enabled those same browsers to support the old-fashioned, table-driven junk markup your grandpappy writes.

But when IE7, with its tremendously improved support for standards, “broke the web,” it revealed the flaw in our beloved toggle. The quest was on to find a more reliable ensurer of forward compatibility. Is version targeting of IE 8 the answer?

"Manufacturers, including Microsoft, have a weird way of staying in business when their products enjoy a healthy market share (healthy for them, if not necessarily for the market). And even huge companies—for instance, companies like Microsoft—occasionally listen to their customers and try to solve problems related to their products."

"Knowledgeable designers and developers—strives to create semantic, accessible, standards-based sites. They also, we hope, aim for great design, compelling and meaningful content, usable interfaces, and semi-transparent site architecture."