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Files categories can be managed by system users only in
Files -> Categories. Clients do not have access to create them.
Clients will only be able to view and filter files by categories in which they already have files assigned.
Each category has a name and description, and optionally a parent or children categories.
Categories administration page
Taking inspiration from WordPress' UI, the categories administration pages features 2 columns. On the left side you will find the existing categories, ordered hierarchically.
On the right side, a double function form that servers both functiosn to create a new category, as well as the editor when modifying an existing one.