The documentation that comes with VoiceAttack v1.7.3 states:
{CMDACTION} - The method by which the current command was executed. The possible results are, 'Spoken', 'Keyboard', 'Joystick', 'Mouse', 'Profile', 'External', 'Unrecognized', ‘ProfileUnloadChange’, ‘ProfileUnloadClose’, ‘DictationRecognized’ and 'Other'.
However, if a command is executed using an inline function(and presumably plugins as well, though I didn't test this) the token will return the value "Plugin" instead.
EDIT: Also applies to the documentation with v1.7.3.1
EDIT#2: Also applies to the documentation with v1.7.3.9; The "Plugin" value is also missing from the documentation for the "Command.Action()" inline function method.
EDIT#3: Fixed with v1.7.5.8