[development] different terms depending on $user data

[Lluís]

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.

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