Velocity and grouvy (XWiki): Programing the interface

Hi all, I have to modify the main interface for editing. Then I have two textarea (using HTMLArea). I would like to program (insert, modify, getting content, synchronize the two textareas, etc). I tried to use Javascript but not efficient for me (incompatible). My question: it is possible in XWiki to program the HTML component with Velocity or groovy. Please any help will be deeply appreciated. Best wishes Youcef