Apple Logic Express 9 - Manual (Page 1114)

Events that do not meet the conditions may pass unchanged to the output, or may be
discarded.
The transformer can also make copies of matching events before altering them, and can
split the selected (matching) events from the unselected ones, via its two top cables.
You must place the transformer in the MIDI signal path in order to use it.
To alter the output of an instrument
1 Cable the instrument output into the transformer (removing the instrument’s internal
port assignment in the process).
2 Choose New > Instrument to create a new instrument, and assign it to the appropriate
MIDI output port.
3 Cable the output of the transformer object into this newly created instrument (which, in
essence, is simply acting as a MIDI output port.
1114 Chapter 37 Environment Objects Reference