So the the third sentence above needs to be re-written. I propose:
This mechanism family offers a number of improvements over the
previous SASL/GSS-API mechanism family: it is more general, uses
fewer messages for the authentication phase in some cases, and
supports a SASL-specific notion of channel binding.
There is no previous SASL/GSS-API mechanism family (the "GSSAPI" mech
isn't a mechanism family, in the RFC 4422 terminology), so I changed
the abstract into:
<t>This document describes how to use a Generic Security Service
Application Program Interface (GSS-API) mechanism in the the
Simple Authentication and Security Layer (SASL) framework. This
is done by defining a new SASL mechanism family, called GS2. This
mechanism family offers a number of improvements over the previous
SASL/GSS-API mechanism: it is more general, uses fewer messages
for the authentication phase in some cases, and supports a
SASL-specific notion of channel binding.</t>