Is it OK if everything looking OK but HTML and CSS are not valid , for CMS Admin/control panel?
Should we only consider Web-standards for site, not necessary for site-management tools?
for example
:http://site.com/wp-admin
:http://site.com/admin/
Is it OK if everything looking OK but HTML and CSS are not valid , for CMS Admin/control panel?
Should we only consider Web-standards for site, not necessary for site-management tools?
for example
:http://site.com/wp-admin
:http://site.com/admin/
Well, the point of standards compliance is to make everything work correctly for every user. Even though admin areas are only accessible to a few select users per site, if you are building a CMS you have to consider that many, many people might use your script which would add additional users who will be needing to access those admin panels. It's best to make everything standards compliant, that's why they create them. If an admin can't get the admin panel working properly, they'll ditch the script.
Some validation errors matter, some don't. The spec is a bit ridiculous in its requirements in places. What is important is that all open tags are closed and they are nested correctly as if this is not done there can be many subtle errors both now and in the future. As for non-encoded entities, using rel's and targets when you shouldn't - it doesn't matter so much.
Since you (usually) can control the access to the admin area (rather than normally having every single device and platform access it) it certainly matters less. The time would probably be better spent adding more features and fixing real bugs rather than aiming for 100% compliance. Don't tell any standards advocates I said that though. :)