[flexcoders] focus in part of editable combox string?

[luoxuanhuayelin]

Hi:
I am looking for a editable combox like this image by using 
actionscript.

'http://img.photo.163.com/aHHUNXTWT0oCr2XiOhY8RQ==/806707283252758320.jp
g' 

For the type of 'TextInput', using the default function 
TextInput.setSelection((3,5), but for 'editable combox' ,I do not know.
Thanks in advance!