Firefox with a "Web Developer" Extension (http://chrispederick.com/work/web-developer/) has a configurable setting for validations. (Note this is not vanilla FF!)
I'd be interested to hear how others are using that with CSE validator and their experiences and suggestions.
In the UI it's at Options / Options / Tools.
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It has a variety of settings for validation. The settings can take a URL or application.
There is also a validation indicator at the top right which shows validation of HTML, CSS and JavaScript. (From the same addon.)
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For the indicator I'd like to hear what others are finding in those results and any indications of how people are being influenced by them.
(There's some embedded images (on the cloud) up there. They're HTTPS and are not showing in my tests. I won't investigate that, but if you grab the source and paste into a browser you can see them.)
Edited after initial publication to explain source of UI items.




