When the "Interactive (use input)" button is checked on the lower "Settings" dialog (accessed by typing cmd-option space, see Fig.24 in §5.2), BP2 keeps listening to messages received on its MIDI input and may react to them if instructed to do so. It keeps listening even whe it is not doing anything particular such as improvizing music or running a script.

Instructions on how to react are stored in a "-in.<name>" file displayed in the "Interaction" window. The format of these instructions is part of BP2's script language, therefore it is convenient to say that the "Interaction" window contains a script.

Conversely, BP2 produces MIDI messages, some of which may be used to trigger processes on external devices (including copies of BP2). For instance, BP2 is able to start any process when prompted by the appropriate MIDI message. This is possible thanks to the instruction

IN On «note» channel «1..16» do «script instruction»

which will execute the specified script instruction at the time a NoteOn message is received, including running another script if «script instruction» is:

Run script «filename»

Caution: this instruction will only work if BP2 finds the specified script (or its alias), either in the start-up directory (the one in which you did a double-click to start BP2), or in the latest directory in which a script was found during the current session. Otherwise, BP2 will prompt the user to locate the script.