World Wide Web Consortium (W3C for Short) is an international standards organization that sets the standards for building and Rendering Web pages, including HTML, CSS, SVG, device APIs, and other technologies for Web Applications.
A W3C compliant page is known to:
- Be Spiderable – search engines can read & rank webpages using programs like robots, bots or crawlers.
- Have better Accessibility – since most of browsers conforms to satisfies W3C compliance.
- Have better Usability – it bears better user experience, even to visually impaired (using screen readers).
- Be fast & optimized – better design, lesser code & optimal HTTP requests.
- Ease of maintenance – since standards are globally recognized.
For a search engine to properly crawl and index your site, it needs to be able to interpret the different elements of your site, such as style, navigation and content. It’s goal is to understand the meaning of the content. Clean, compliant, expected HTML and CSS code make it much easier for the search engines to determine what is content and understand the meaning of the content.
For this, you can use the online W3C Validator tool
At the same time, you should also keep in mind that 100% compliance could be pretty difficult to achieve. If you run your validation and you end up with some warnings, or maybe just an error or two that isn’t a high priority you will be okay.