I frequent the [css](https://stackoverflow.com/questions/tagged/css "show questions tagged 'css'") tag often and many questions are tagged both with [css](https://stackoverflow.com/questions/tagged/css "show questions tagged 'css'") and [css3](https://stackoverflow.com/questions/tagged/css3 "show questions tagged 'css3'"). 

Leaving aside other common mistags ([html5](https://stackoverflow.com/questions/tagged/html5 "show questions tagged 'html5'") on a generic [html](https://stackoverflow.com/questions/tagged/html "show questions tagged 'html'") question etc), when is appropriate to retag a [css3](https://stackoverflow.com/questions/tagged/css3 "show questions tagged 'css3'") question to simply [css](https://stackoverflow.com/questions/tagged/css "show questions tagged 'css'")?

Should [css3](https://stackoverflow.com/questions/tagged/css3 "show questions tagged 'css3'") be used only for questions regarding problems with functionality added by CSS3 specifically?  

The list [from MDN](https://developer.mozilla.org/en/docs/Web/CSS/CSS3) includes, but is not limited to:

* opacity & rgba
* numerous pseudoclasses (`:enabled`; `:disabled`; `:checked` etc)
* media queries
* new values to existing properties (`background-attachment: local` etc)

and many more.