[development] different terms depending on $user data

I need groups of users sharing a taxonomy, but not terms; the group is defined depending on their user profile; so I have been able to write a module using hook_node_grants and hook_node_write_perms to separate their content; but now I need them able to categorize it. So a user inside "one group" should be able to add terms (if their permissions allow him to do so) and that term should only be visible to his group. Any hint of how to achieve this is welcome. -- *La vida és com una taronja, què esperes a exprimir-la? *Si creus que l'educació és cara, prova la ignorància. *La vida és com una moneda, la pots gastar en el que vulguis però només una vegada. *Abans d'imprimir aquest missatge, pensa en el medi ambient.