"selected text choice" means the user press "Enter" key or double click on
one of the line in the propose list. For example, the content assistant
popup window has a propose list of 10 choices. The user selects the 3rd
choice. How can the program detect that the 3rd line in the propose list
is chosen? It is too late to find the added text by scanning the document.
I do not see any available class/interface in content assist package to
provide this function. So I am trying to find out an efficent way to do it.