All HTML, XHTML and CSS code fully compliant with the World Wide Web Consortium (W3C).
W3C compliance ensures:
•Your website is accessible for the disabled
•Your website can be accessed from a number of devices, from different browsers to mobile phone users
•Your website will look and function in a similar way regardless of the browser, screen size of device.
•The code within your site is reduced, therefore reducing download speeds.
•Search engine spiders are able to read the whole page, and find the links to the rest of your site.
Following W3C guidelines ensures that your website has the best possible chance of being viewed correctly on different web browsers and computer platforms, since all browsers aim towards compliance with existing HTML and CSS standards.
If a designers code is not compliant and there are errors in a web page, browsers typically try to compensate in different ways. Hence some browsers may ignore the broken elements while others make assumptions about what was trying to achieve. When a search engines visits your page and tries to read them for keywords, they will also have to make certain decisions about what to do with the errors. Like browsers, different search engines will make different decisions about those errors which can result in certain parts of your web page (or perhaps even the entire website) not being indexed.
In addition to validating all XHTML and CSS code with the online W3C validators I also test on both a Windows PC and Apple Mac using Internet Explorer 7 (Windows), Internet Explorer 8 (Windows) Firefox (Windows and Mac) latest versions, Safari (Mac) latest version, Comino (Mac) latest version, Chrome (Windows & and Mac) latest version. This ensures that your website will be views as designed by the majority of website visitors. If you have any other specific requirements let me know.
Once we're done you'll be left with a compliant site that not only will be available on a much larger number of browsers (increasingly important as browsers such as Firefox gain more and users) but you'll have a site with far less code that will rank higher on the search engines because of it.
To be sure, W3C validation is not the "magic bullet" to top rankings. In the current SEO world there is no one thing that is. However, as more and more website are born and the competition for top positioning gets more fierce it's important to take every advantage you can to not only get to the first page but to hold your position against those who want to take it from you as you took it from someone else.