[CSS21] 4.4. Decoding style sheets using the referring style sheet or document

The fourth step of style sheet encoding detection steps specified in section 4.4 is :

        4. charset of referring style sheet or document (if any)

Specifically, what is the exact meaning of the "(if any)" clause ?

Does it mean :

a. "If the charset specification of the referrer document exists " e.g. a Content-Type charset metag, a charset attribute on the referring link element or an @charset rule defined this charset explicitly.

Or...

b. "If any referred document exists"