Question

May websites, including professional ones usually have a “W3C Markup Validator” and “W3C CSS Validator.” Why do you put them there? Is it just pride or is it justified? If it is more than pride, what justifies them?

Answer 1

The purpose of these W3C valid badges is:

To show readers that one has taken some care to create an interoperable Web page, a “W3C valid” badge may be displayed (here, the “valid XHTML 1.0” badge) on any page that validates.

But the usage is restricted:

Web content providers are granted the right to use the “W3C valid” logo on pages that pass validation (through the use of the W3C Markup Validator) for the W3C technology represented by the icon, and only on pages that pass validation. The icon must be used as a link to revalidate the Web page, thus providing a way to verify the page author’s assertion that it passed validation.

[…] the icons are only a mechanism to identify pages that have been determined to be valid, and to easily revalidate pages as often as as they are modified.

So these badges are intended to be used to easily revalidate the page the badge is on to prove the promise you make by placing it on your page (if they really think validity is an honorable achievement rather than a matter of course).

But the funny thing is that Opera’s MAMA project found that not even 50% of those pages that had such a banner were actually valid. In that case such a badge is rather a self-humiliation, pointing the readers to something they wouldn’t have noticed themselves.