Section " 5.2.1. Working Group and Interest Group Participation Requirements" contains:

As a courtesy to the group, if the substitute is not well-versed in the group’s discussions, the regular participant should authorize another participant to act as proxy for votes.

It isn't clear to me whether this introduces a 3rd individual, in addition to the regular participant and the substitute.

Also, it isn't obvious to me why this is a courtesy to the group. As courtesy to a group, I'd expect more something along a heads-up or notification of a situation.