How to get the modified portion of text in a TextArea

i need to know which part of the text is been modified by the user inside a Flex TextArea. I'm listening to TextArea's Event.CHANGE and my code run on everychange but i don't know what the user have done to the text and it's too long to process it again at every keypress or paste

We are still with Flex 3.5开发者_运维问答 but i may consider Flex 4 if the solution is easier.

Thanks a lot

Consider using focusOut and firing your function when the user leaves the text area.