' MyListBox class
INHERITS ListBox

PRIVATE $cPos AS NEW Collection
PRIVATE $aKey AS NEW String[]
...

' Reimplements the Add method
PUBLIC SUB Add(Text AS String, Key AS String, OPTIONAL Pos AS Integer = -1)

  ' Adds the item to the list box
  SUPER.Add(Text, Key, Pos)
  ' Adds the key to key array
  IF Pos \< 0 THEN
    $cPos.Clear
    $cPos[Key] = $aKey.Count
    $aKey.Add(Key)
  ELSE
    $aKey.Add(Key, Pos)
  ENDIF

END
...