ui/src/main/java/ucar/util/prefs/ui/Field.java
protected boolean accept(StringBuffer buff){
     if (!validate(buff)) {
       validate(buff);
       return false;
     }
     if (acceptIfDifferent( getEditValue())) {
      setStoreValue( validValue);
      sendEvent();
     }
     return true;
   }
protected boolean accept(StringBuffer buff){
     if (!validate(buff)) {
       validate(buff);
       return false;
     }
     if (acceptIfDifferent( getEditValue())) {
      setStoreValue( validValue);
      sendEvent();
     }
     return true;
   }
Get current value from editComponent, save to store.
If different from old value, fire PropertyChangeEvent.
Return false if invalid format, add error message to buff if not null.