This has been discussed in length on a number of forums lately and results in some interesting arguments whether or not validated HTML goes to help boost your rankings in Google. HTML Validation is conducted to check for errors using a tool such as the W3C Validator. For the most part I am believer in validated xhtml/html and the benefits it mainly has from a good design point of view. Once I changed over to XHTML I never looked back. It's good technique in my opinion of a professional website. Has it helped in boosting my rankings? Well I can't say for sure, but I would argue that it has aided in the success of obtaining top rankings. However is it necessary? Not completely. Often times an unvalidated page can outrank a validated page and vice versa. But consider this, Google will spider a page regardless even if it has bad HTML, but bad HTML can cause the page to be displayed incorrectly. If this is the case then Google may not get the correct interpretation of the pages meaning. It also has side effects that can affect users who visit the site. I think its just common sense that if you create a page to rank in the search engines, you also make sure that others can view it as well.
One of the members Brian I, gives a good example that you can "Try [testing] it by deleting the tag from a page, or the end quotes from a URL in an anchor". What happens is not going to give any search engine a good impression about the page. But when talking about specific bad HTML we are often talking about minor errors that can occur in the code, such as not closing a bold tag, or forgetting to close an element. You might also code an "a href" tag in correctly, and so on.
Another member Shor goes into more detail about this answering some questions that I would agree with:
Will it validation count towards higher rankings in the future? No, as search engine technologies are inclined not towards 'studying' code but towards document semantics and a document's relevant domain. In other words, search engines are being engineered to follow more natural human thinking processes and patterns, Which I find a little ironic as SEOs are trying to figure out how to best assimilate themselves closer to SEs (and their algos) while the SEs themselves are trying to evolve towards human user search patterns! Sounds like a Benny Hill chase scene.
So what's the point of validation? Chris_D's analogy is succinctly appropriate. Should you have validated XHTML to boost rankings? No. Should you have validated XHTML? Damn straight you should - the standardisation that validated XHTML offers is a vital ingredient of professional web development.
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