An interface or its children can be altered programmatically in many ways. This chapter describes APIs for the most common of these.
By default, each CAPI interface runs in its process. It is important to understand that an on-screen interface and its elements must be accessed only in the process of that interface. In most circumstances the user alters the interface by a callback inside the interface, which will automatically happen in the correct process. However, calls from other processes (including other CAPI interfaces) should use execute-with-interface,
execute-with-interface-if-alive, apply-in-pane-process or apply-in-pane-process-if-alive.
CAPI User Guide and Reference Manual (Macintosh version) - 3 Aug 2017