action perform action event action perform object sourc sourc sourc uml combo box modifi awt event mous event mask uml combo box combo uml combo box sourc object combo select item object tag valu combo target model facad model element model facad tag valu tag valu object old model facad model element tag valu model extens mechan helper remov tag valu old tag valu model extens mechan helper add tag valu tag valu 