Xtend now keeps track of the state of all X10 devices. This allows
you to have conditional execution of commands (e.g. "do this only
if lights A1 and P7 are on"). This data is also made available to
all programs run by Xtend and to any interested process running
on the computer.

Information made available to programs:

On/Off status for all 256 devices
Addressed / not addressed status for all 256 devices
Appliance or light for all 256 devices