The predicate for whether a pinboard-object is in the highlighted state.
pinboard-object-highlighted-p tests whether the argument is in the highlighted state. The state is switched by calls to highlight-pinboard-object or unhighlight-pinboard-object. In graph-pane and tracking-pinboard-layout, the state switches automatically, but in other panes it happens only by your calls to highlight-pinboard-object or unhighlight-pinboard-object.
pinboard-object-highlighted-p is useful when the draw-pinboard-object method also does the highlighting, so needs to decide if the object is highlighted or not.
CAPI User Guide and Reference Manual (Windows version) - 3 Aug 2017