Whenever I’m developing a new website and I encounter something that just doesn’t look right when I compare how it renders on different browsers, one of the first things that I check is the !DOCTYPE of the document.
There’s been a major push in recent years for websites to validate, that is the code behind them should be written to a standard, that follows the proper rules as set by the World Wide Web Consortium (W3C). And one of the conditions for a webpage to validate is that it contains the correct Doctype for the kind of page that it is presenting. The Doctype essentially tells the browser which rules to follow when rendering a page on the screen. (And you thought that web browsers were simple pieces of software!)
The page author, Matthias Gutfeldt, has presented a very useful, usable table indicating how different web browsers handle each Doctype declaration. I have ‘printed’ this page to PDF to keep on my PC as a resource, even when I’m not connected to the Net — I’ve copied it to my Psion too. A fine resource.