What is a Gnostic Gospel?

Pheme Perkins ("What Is a Gnostic Gospel?" CBQ 71.1 [2009]: 123) writes:

"What is a Gnostic Gospel? Used in the oral sense for preaching a message about salvation revealed through the coming of Jesus, it is the content of their soteriology, not the term, that distinguishes Gnostics from other Christians. Used in the mid-second century forward for written accounts of Jesus and his teaching commonly circulated among Christians, there is no special Gnostic Gospel. Gnostic teachers rely on the range of gospel traditions being circulated among Christians with no greater tendency than believers to exploit apocryphal Gospels. In addition, the poetics of the Gnostic universe push its teachers away from imaginative engagement with the historical or physical world such as might produce additional Gospel narratives. Instead, one has a form of writing that Plese refers to as 'meta-physical fiction,' though one might expect more narrative to justify the 'fiction' in such a description'."