[Plugin: WP-reCAPTCHA] reCAPTCHA is not xhtml 1.0 strict compliant

I installed the latest version of reCAPTCHA and everything works fine. However the comment page is no longer xhtml 1.0 strict compliant. Even after I checked the “make it compliant” checkbox in the wordpress setting.

Here’s an example:

http://validator.w3.org/check?uri=http%3A%2F%2Fpure-essence.net%2Fwp-themes%2F%3Fp%3D57

The validation error says:
there is no attribute “aria-required”.

…size=”22″ tabindex=”1″ aria-required=’true’ /

What is aria-required attribute for?