All CAPI elements (panes and pinboard-object) inherit from capi-object. This includes a plist, which can be accessed by capi-object-property, (setf capi-object-property) and remove-capi-object-property. There is also the accessor capi-object-plist.
CAPI object property is a very convenient mechanism to add slot-like behavior without having to define your own class. For example, it is used for caching the images in:
(example-edit-file "capi/choice/list-panel-drag-images")
A capi-object also has a name, which can be used to give it a unique identifier. You can set name by the initarg :name, and access it by capi-object-name.
CAPI User Guide and Reference Manual (Unix version) - 01 Dec 2021 19:32:40