question

The Perspective view has an OnMenuPopup node (VIEW:/standardviews/documentwindows/Perspective>eventfunctions/OnMenuPopup)

that uses code like this:

var popupMenu = getviewmenu(c, 4);
treenode selObj = selectedobject(c);
int validSelObj = objectexists(selObj) && selObj.dataType == DATATYPE_OBJECT;
int editMenuIndex = menupopup(c).subnodes["Edit"]?.rank - 1;
menugray(popupMenu, editMenuIndex, !validSelObj);