Text under selection

How can I get the text under the selection.

for example I write:- Text layout framework and I select only the word layout from the whole sentence.now how can I get this selected text.

I have worked with following way but it returns me the whole sentence(span element) rather the selected range.

if(editManager.activePosition != editManager.anchorPosition)

{

     var Range:ElementRange =  ElementRange.createElementRange(textFlow,editManager.anchorPosition, editManager.activePosition);

}