While most Web browsers do an increasingly good job of parsing poorly written HTML HTML is an acronym for Hyper Text Markup Language. It is a markup language that is used in the development of web pages and websites., some errors are not always caught gracefully. If your site behaves unpredictably when viewed using different web browsers, you may want to run your site though a validator.
All web sites — including those generated by WordPress — use common languages (HTML, CSS CSS is an acronym for cascading style sheets. This is what controls the design or look and feel of a site., Javascript JavaScript or JS is an object-oriented computer programming language commonly used to create interactive effects within web browsers. WordPress makes extensive use of JS for a better user experience. While PHP is executed on the server, JS executes within a user’s browser. https://www.javascript.com/., RSS etc.) to “tell” web browsers what to display and how. In order to ensure that these languages are used and interpreted correctly, a number of organizations (such as the World Wide Web Consortium) develop and maintain standards. These standards define how the languages should be used in a web page and how browsers should interpret them.
One analogy for this would be music scores — a universally recognised method for conveying audio information on paper that has been around for hundreds of years. A piece of music that has been correctly transcribed in this fashion can then be performed on many different instruments. But this only works because everyone uses the same rules when transcribing music. The same applies to web pages (the music score) and web browsers (the instruments). Unless web pages follow the rules, the outcome is likely to be poor when they are viewed in different browsers.
Validating a website is the process of ensuring that the pages on the website conform to the published standards. It ensures that your web pages have the best possible chance of being interpreted correctly across the greatest range of software.
The World Wide Web Consortium (W3C The World Wide Web Consortium (W3C) is an international community where Member organizations, a full-time staff, and the public work together to develop Web standards.https://www.w3.org/.) offers a number of free, online, validator tools: