[editing] Suggested selection.extend can not select based on how the text currently displayed

Dear all,
 
My interpretation of the suggested selection.extend is that it can not select based on how the text is displayed. I'm thinking in particular of the feature to extend to the lineboundary, like this:
var selectionPoint = window.getSelection();
 selectionPoint.modify('extend','backward','lineboundary'); Supported by most browsers (not IE) this could be used to for example select or highlight a line of text that the user clicks on. This feature can have both practical and accessibility uses. 
 Best regards, Erik