In fact I've several cases with this problem :
My first example :
I want to built a graph :
1/ I edit the graph
2/ I add some state
3/ I add transitions wich needs the collection of state previously add to the graph
=> lukas have understand I think my problem... it's very usefull to have a
description "instance side"...
Steph : it's does not make sens to do this with meta level?