Conceal faction [635]
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Usage:  automatic when necessary

Knowledge of 635 causes a character to keep its faction affiliation
secret.  Other units attempting to learn the what player the unit
belongs with the skill Determine character's lord [9521] will fail.

Permissions set for the player of a character concealing its faction
affiliation will not include the character.  For example, suppose
unit [5499] is concealing the fact that it belongs to player [613].
Permissions declared for player [613] (such as ADMIT, DEFEND, etc.)
will not include the sneaky unit [5499], since [5499] will not admit
to an affiliation with [613].

Furthermore, such units will not DEFEND units from their own faction
by default, since this might reveal their identity.