Question : HTML 5: resize

1) After drag and drop class diagram (I already know how to do it), and then resize the diagram.  This feature is similar to UML tool drawing sequence diagram. After you drag and drop(dnd) the class, there is vertical line which could be extended by user. Shall I response to some event, then check the mouse position?    

Answer : HTML 5: resize

if you are ok with jquery solution, then check this also
http://dev.iceburg.net/jquery/jqDnR/