Dokumentation for acpid can be found in 'man acpid'. Be aware that the acpid is only used to hand over ACPI events (caught from /proc/acpi/events) to other services (e.g. hal, powersaved, iald, ...). The events are handled by those services. Most of them are processed by the powersave daemon. For further documentation, please have a look at: /usr/share/doc/packages/pm-utils/ or http://powersave.sourceforge.net/