Just want to say that I'm studying the code here :
There is a LOT I have to learn but, withe help of the debugger, it helps a lot.
So far, I ran the code at the above link and I can see that this partly does what I need to do, which is to return some values in response to a mouseover movement over some graphic object. To wrap one's brain around the used symbols is not for the faint of heart... Needless to say, I'm discovering a whole world but I'm not totally lost, programming wise. I just have not a "mental" map of Matlab's object model... But I'm getting there.