w3 validation errors - please correct ASAP

Those aren't errors we will fix. The SCLogin conforms to the HTML5 spec, which all major browsers support. It's (generally speaking) a replacement of the XHTML spec as it defines more accessibility elements (like the aria tags reported above) and is a more web-browsing specific spec instead of a more generic spec for representing any type of data.

The XHTML spec is a much more rigid specification that defines the 'base' elements. HTML5 extends XHTML and adds a lot more elements for improved control and description of webpages, including the newer things like the <audio> and <video> tags.

You can even get a general sense of what the spec recommends for webpages by the declaration types:
XHTML Transitional:HTML5:It should be pretty apparent that, for html sites, HTML5 is the recommended choice.

I hope that helps explain, but if you have any other questions or feedback, please let us know!

Finally, we're very glad to hear you like the SCLogin module so much. If you haven't already, please consider leaving a rating and review for SCLogin, or our support, on the Joomla Extension Directory. It certainly isn't required, but is very appreciated:
extensions.joomla.org/extensions/access-...authentication/24054

Thanks,
Alex

Oh yeah, for more information and background on the HTML 4.x tags (like XHTML Transitional) and the HTML5 tag, see:
www.w3schools.com/tags/tag_doctype.asp

All the best,
Alex

No problem for the explanation.. we'd rather you understand our reasoning than simply putting our foot down and saying 'no'

As for testing, you can use the "More Options" selector of the validator tool and force HTML5 as the doc-type. You'll still run into errors, but there should be less/none from the SCLogin module. I just tried from your page, and the error count increased, but mainly because you're using older table styles that are no longer recommended in HTML5. Of course, they still actually work in HTML5. It's not truly backward compatible, but most browsers will recognize and render older styles for obvious compatibility reasons.

Finally, for the HTML5 experimental label, it's true that it's not finalized yet.. however, HTML5 has switched (formally) into a 'living document'. It isn't planned to be ratified until something like 2018.. until then, it will be informal with new things added, but what's there is pretty darn stable and, again, the core featureset is supported by all major browsers.

As always though, if you have any other questions or feedback, just let us know. We'd love to read your review of the SCLogin module on the Joomla Extension Directory as well:
extensions.joomla.org/extensions/access-...authentication/24054

Thanks,
Alex

Thanks for the great review. We definitely appreciate it and can always use more. They really do help.

As for the HTML5 warnings, I actually only see 2 (though I may have missed some since there were quite a few):
* Line 315, Column 58: Attribute alt not allowed on element input at this point.
That's probably a valid error and a tag we shouldn't be using
* Line 301, Column 436: The aria-labelledby attribute must point to an element in the same document.
That also is likely an issue with the SCLogin that we'll need to fix.

Beyond that, I think the SCLogin actually conforms well with the HTML5 spec... and, even those 2 problems shouldn't cause a real problem.

Thanks again for your feedback and should you need anything else, just let me know.

Thanks,
Alex