Ok, thanks.
Out of interest, do you know what the consequences are (if any) of using invalid mark-up such as I've done?
this is an interesting question to me, as i've just had a long conversation about standards and such with several people. here's my opinion and some technical viewpoints, and several of those people seemed to agree with me. there were also some who argued against it...
if you are looking to have your page viewed only by browsers on a traditional computer, there are no consequences to not validating. however, if you want this to scale to handheld devices and such, some of the browsers on those will not parse the content correctly unless it validates against certain standards. i wish i had specifics on which browsers/devices/standards combinations required what, but i don't know of an exhaustive list anywhere, unfortunately.
that is the reasoning behind the newer standards, especially XHTML. newer standards are more for the future than now. by sticking closer to a standard, the browser doesn't have to worry about closing <p> tags for you, knowing when a break tag ends (<br> should be <br />), and be concerned about all the different "possibilities." This makes the codebase smaller, more efficient and easier to fit on smaller-capacity devices. if the browser knows exactly what to expect, it only has to look for that and doesn't have to worrying about assuming what you might (or might not) have wanted to do. and if something doesn't fit in the standard, it just rejects it. think parsing xml, which is exatly what is going on.
sticking to standards also (theoretically) helps to keep content appearing consistently in all browsers (on traditional computers in the context of this paragraph), but anyone who has worked in this field knows this just doesn't happen.
i would hope more people would join in this particular discussion. i'm very interested to hear what people think about this subject.