Here's a silly but workable work-around:

 Code:
Function ComboBox1_TextChanged($sender, $e)
 Select
  Case $sender.text = "a" 
   If 1 
    $Sender.Text = "You pressed A"
   Endif
  Case $sender.text = "aa"
   ? "aa detected"
  Case $sender.text = "aaa"
   ? "aaa detected"
 EndSelect
EndFunction