[plt-scheme] What to augment, how to highlight ?

Hello,

I have two new questions :

- Iam making a little text editor. So, i want to get the line-number.
In a text%, the method is "last-line" (i use color:text% who has some
little more functions). But this only return the value.
My goal is to put this number in a message% when an event (keyboard-
event, mouse-event, ...) occurs.
But i don't find which function i must augment. I thought on-event and
on-char, but no. They can only be override.
Very few functions can be augment, and none does what i want. Someone
has an idea ?

- My second problem is about highlighting.
Iam trying to highlight a text (some keywords). So i think to use a
color:text% from framework.ss
But i don't understand how to use the "start-colorer" procedure. Some
has an example ?

Thanks,
Laurent