When url() contains escaped code points in url it is tokenized as a function token

[romainmenke]

\75 Rl(foo)

This is equivalent to url(foo)

The first is tokenized as a function token, followed by an ident and )
The second is tokenized as a url token

https://www.w3.org/TR/css-syntax-3/#consume-ident-like-token

It appears as if the check for a url function name is done against the raw value instead of the unescaped ident sequence value.