W3C has released Unicorn, a one-stop tool to help people improve the quality of their Web pages. Unicorn combines four popular tools, including the Markup validator, CSS validator, mobileOk checker, and Feed validator, with a single interface. This means you can check a Web page with a visit to one url instead of four. Unicorn allows you to choose all four validation checks at once, or any one of the four individual checks as needed.
Unicorn allows the same three ways to validate your Web site as the individual tools, i.e. you can submit a url to the page to be tested, upload the files, or enter (cut-and-paste) the code directly into a text box.
Validation, like unit testing, is the foundation of quality assurance. Standards compliance is facilitated by validation and, in turn assures the overall quality of the Web page / web site. Validation can, however, be a tedious and costly process, particularly in cases where you are trying to bring an existing site into compliance.
Simplification of the tools used to test validation and compliance contributes to reducing the overall cost and workload. Performing four validation tests simultaneously, which is what Unicorn delivers, definitely simplifies the validation effort when compared to submitting the same file to four different validation testers.
If you are in the position of creating a new Web site, use of validation tools as each page is developed makes the same kind of sense as unit testing. If you are charged with improving or maintaining an existing web site, crafting:
... one that complies with standards such as HTML, CSS, or the Web Accessibility Guidelines, is the right thing to do, and is also a profitable choice. Guidelines and tools are readily available to help you create a Web site that conforms to Web standards, ensuring a broad audience, cost-effective development, and easier maintenance.
The quote is from an article by the WC3 Quality Assurance Group.
Being the right thing to do, does not make it easy. A strategy is required.
But deciding how to convert an existing site to a standards-compliant format is a difficult decision. Your site may have legacy, unmaintained documents in multiple formats or may serve a large amount of documents, making it difficult to update. Your site may be backed by good design and flexible technologies, which will simplify the task, yet in any case updating the site will require a resource commitment.
There are two typical ways to make an existing Web site standards compliant: start completely over (the wrong way), or manually validate each page (the hard way).
The article goes on to discuss the two approaches, analyzing why they are wrong, and suggesting a third approach: systematically updating one section at a time.
The use of validation tools, like Unicorn, is but one necessary step in the overall quality assurance process. [It should be noted that some validations - Americans with Disabilities Act (ADA) compliance for example - are not amenable to automated validation testing.]