I can guarentee you it is accurate Gabbe. Why can I guartentee this? Because WC3 CREATED HTML. They are the head honchos, the top of the food chain. Of course, they are also very strict. Let me explain part of it with using google.com as an example:
The first note is that google checks for HTML 5 compatibilities, which is currently a very new reign (which I am having fun learning), supported only by firefox and webkit browsers such as safari, each only to some degree. NO browser has it completely implimented, so WC3 notes the user of that.
The first error is about encoding type. Google checks for your browser and operating systems when you use the site, so it can deliver accurate character sets. Of course, this is not a universal character set, and is really meant for windows, since it is NOT a standardized (notice it's not an iso) charset, thus WC3 raises a flag.
Secondly, because google is using strict syntax in HTML 5, the table tag and all its child tags (td, tr, th) are technically depreciated, in favour of moving to div tags with CSS. Most people, me included, have not fully made this transition. The main downside to table tags that provoked them to move away from them is that a web browser must read the entire table tag (all the way to its closing tag) and cannot render anything until it has the entire table (because even a slight change in the very last tr tag can affect the whole table). Tables actually have to be read through twice, once for the tags and once to render the data. CSS is a lot harder and more complex coding, but allows linear rendering. Of course, table tags are slightly more compatible, since VERY old browsers do not support CSS well.
There's also various attributes that google uses, presumably for compatiblity (as I said, older browsers cannot use CSS that well), such as bgcolor, which are best done as a css style (either as a class/id and referencing that in an external CSS, using an entire tag in an external CSS, or by means of the style attribute). For example, an inline css tag for bgcolor would be style="background-color: #fff".
Another common error is that Google frequently links to links with GET values (everything after the ? is really a variable, with the variable name on one side of the equal sign, and the variable data on the other, then with the & sign separating variables. Of course, this was ONLY originally meant for forms, so when sites use those variables, such as for a CGI or PHP script to read (this is how they store your search data), so google raises a flag there. Instead, & signs that appear normally in the text are used to make special symbols, such as < being '<'. Fortunately, links are not affected by these symbols, so it is fine to use them for this, and with common place techniques such as URL redirects with PHP/CGI scripts using these variables, its not a huge deal.
Lastly, for some reason, google does not close its script tag at the end of the file. Most likely this was negelected, purposely (because of server generated data) or accidently because of a overlook by the coder. That's actually one of the biggest errors on the page, but most, if not all, browsers detect and fix this client side, though it is still bad coding.
Now, many sites use "bad" coding practice because the new standards are either more difficult to use or aren't so well on very old browsers. So what is an example of a good site? Check the index of the forum board! There is ONE error and that is totally my fault (I forgot the type attribute when I made some javascript for the automatically updating clock in the top right corner of the theme, and will have to fix this for the next version in order to maintain the XHTML logo at the very bottom of the page (this logo shows we passed this verification)).
