These specs are for CSS files that are imported by Sass, using @import "foo" to import foo.css. These files should be parsed as plain CSS, and should not allow any Sass-specific features.

As a rule, anything in the plain CSS files that would be interpreted differently if it were SCSS should produce an error. Although some of these could theoretically be valid CSS, such as @import url("#{foo}"), it's much more likely that they're a mistake on the user's part that they should be notified of.