This attribute stores the address of the icclass object's target object.
Whenever the icclass object receives an om_notify or om_update message, it
forwards that message to its target in the form of an OM_UPDATE message.
If the icclass object has an attribute mapping list (see the ica_map
attribute below), it also maps the om_notify/om_update message's attribute
IDs to new ones before forwarding the message.

If the value of ICA_TARGET is ICTARGET_IDCMP, the icclass object sends an
idcmp_idcmpupdate intuimessage to its window instead of forwarding an
OM_UPDATE message.  See the rootclass description of om_update for more
information.