The specification : string( <custom-ident> [ , [ first | start | last | first-except] ]? )

For the string() property, W3C specifications indicate that first is the default value of the second argument. So string(<custom-ident>) must behave like string(<custom-ident>, first).

For now, it behaves like string(<custom-ident>, first-except).

HTML: string-default.html

Result: string-default-wrong.pdf

The result we should get: string-default-correct.pdf