Ksp reference Manual

Event Status Constants
$EVENT_STATUS_INACTIVE
$EVENT_STATUS_NOTE_QUEUE
$EVENT_STATUS_MIDI_QUEUE
%GROUPS_AFFECTED
An array with the group indices of those groups that are affected by the current Note On or Note Off events.
The size of the array changes depending on the number of groups the event affects, so use the 
num_elements()
command
to get the correct array size.
The returned indices come before any allow or disallow group commands, and so it can be used to analyze the mapping of
the instrument.
$NOTE_HELD
1 if the key which triggered the callback is still held, 0 otherwise
%POLY_AT[]
The polyphonic aftertouch value of the specified note number
$POLY_AT_NUM
The note number of the polyphonic aftertouch note which triggered the callback
$RPN_ADDRESS
The parameter number of a received rpn/nrpn message (0 – 16383)
$RPN_VALUE
The value of a received rpn or nrpn message (0 – 16383)
$VCC_MONO_AT
The value of the virtual CC controller for mono aftertouch (channel pressure)