This page refers to the Control Panel's side-bar navigation. Not to be confused with "Navs", where you can create trees to be used for the front-end of your site.
Accessing CP Nav Preferences
Users can access CP Nav preferences through the cog icon in the upper right hand corner of the CP.
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Customizing CP Nav Preferences For Other Users
In order to customize CP nav preferences for other users, you must first enable Statamic Pro, and you must either be a super user or have permissions to manage preferences.
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This will allow you to customize the default CP nav for all users, or on a role-by-role basis, though end-users will still have the ability to further customize their own CP nav as they see fit.
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Extending Via Addon
On top of allowing the end user to customize their CP nav, Statamic also provides PHP helpers for extending the CP navigation within an addon.