Controlling access to category by group
Da'ud Vyd wrote:
How does Tikiwiki handle category permissions when a page has multiple categories
I think Tiki uses category permissions in an OR way, and you want it to work as an AND i think (i.e. view permission should be granted if they have user category AND topic category AND project category)
Generally i would advise against using permissions on different category trees as it can get so complex and quickly can become very difficult to maintain (although the permissions display module Bernard mentioned helps now)
You might like to look at Roles and Templated Groups to see if that might fit your use case. I used it on a recent project and it seems all work ok, but is quite tricky to set up correctly, we have some feedback and another example to add to the documentation one day... but not today sorry 
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