Every Search Engine Robot Needs Validation
Your website is ready. Your content is in place, you have optimized your pages. What is the last thing you should do before uploading your hard work? Validate. It is surprising how many people do not validate the source code of their web pages before putting them online.
Looking at what your visitors and the robots need, you can easily see how making your website "search engine friendly", also makes the website visitor friendly.
For example, one project I worked on had many validation problems. Because of the huge number of errors generated by problems in the source code, the search engine robots were unable to index the web page, and in particular, a section of text with keyword phrases identified specifically for this page. Ironically, human users had problems with the page as well. Since humans are smart, they could work around the problem, but the robots could not. Fixing the source code corrected the situation for human and automated visitors.
There are several tools available to check your HTML code. One of the easiest to use is published by the W3C (http://validator.w3.org/). While you're there, you can also validate your CSS code at W3C's page for CSS (http://jigsaw.w3.org/css-validator/). The reports will tell you what source code needs to be fixed on your web page. One extra or unclosed tag can cause problems. With valid code, you make it easier for your human visitors and search engine robots can travel through your website and index your pages without source code errors stopping them in their tracks. How many times have you visited a website, only to find something broken when going through the web pages? Too many too count, I'm sure. Validating your pages makes everything easier for your website to get noticed.
As I said before, what works for your website visitors works for the search engine robots. Usability is the key for both your human visitors and automated robots. Why not provide the best chance for optimum viewing by both?