I suspect the intended production is <url>, which also accepts <src()>.

https://drafts.fxtf.org/motion-1/#typedef-offset-path

Aside

<url()> and <src()> are never defined with their own production rules:

The <url> type, written with the url() and src() functions, represents a URL, which is a pointer to a resource.

The syntax of <url> is:

<url> = url( <string> <url-modifier>* ) |
        src( <string> <url-modifier>* )

For legacy reasons, a url() can be written without quotation marks around the URL itself, in which case it is specially-parsed as a <url-token>

https://drafts.csswg.org/css-values-4/#url-value

Therefore I considered <url-token> as a replacement of <url>, instead of increasing maintenance cost with a "custom" production rule.

Ideally:

<url> = <url()> | <src()>
<url()> = url( <string> <url-modifier>* ) | <url-token>
<src()> = src( <string> <url-modifier>* )