It is possible to perform standard edit actions like copy and paste on the current active element, which is not necessarily a CAPI pane, using the functions active-pane-edit-function, for example active-pane-copy.
These functions find the active element and try to perform the operation on it. The active element can potentially not correspond to a CAPI pane, for example when prompting for a file the active element is somewhere in the dialog, which is a standard dialog of the windowing system rather than being a CAPI interface.
It is also possible to define what edit operations do when they are called on a pane in an interface class which you have defined, by specializing the pane-interface-* methods such as pane-interface-copy-object. For choices, there is also item-pane-interface-copy-object. Typically these methods will need to access the system clipboard, using set-clipboard and clipboard (see 18.6 Clipboard).
CAPI User Guide and Reference Manual (Unix version) - 01 Dec 2021 19:32:35