By testing our code with the W3C validator, we can find mistakes and errors with suggestions on how to solve the problems.
Using a library because it is popular is not responsible. You should use a library or a framework based on the needs of the application. Popularity is one of the factors but not the only factor to consider in choosing a library and a framework.
Make sure you put emphasis when there are errors on the forms, so your user can know exactly where the error is to fix it.
The following browsers support this feature: Opera 9.5+, Chrome, Firefox 3.5+, and Safari 1.1+. Historically, this feature was only supported by Safari, but now all recent major browsers support this property except IE.
Remember that 90% of the time people are looking for information when they enter a website, and they are looking for that information immediately.