[horde] Adding content from other modules into Turba

[Carl-Philip Hänsch]

Hello,

I have the following issue:
I wrote a module that is able to send old-style letters.
To select a recipient, I want to involve Turba. When looking at a  
profile in horde/turba/contact.php?source=...&key=... I want to add a  
button under the address that opens my module and starts a letter. The  
address of the recipient should be filled in of course.

How can I achieve that?
I talked to yunosh and he told me that I have to add a field of the  
type "html" to turba and then write a getter for that field. The way  
to do that is to register that field somewhere in backends.local.php  
in turba and then add the getter somewhere in hooks.local.php.

Can you please tell me where that "somewhere" is? I just see a bunch  
of backends for turba like the sql backend and such, but how can I add  
a field for all backends?