Content is the Horde tagging engine. It stores tags, references to the objects they are applied to and keys for the users who applied them. Any Horde application can tag arbitrary objects (contacts, events, tasks, bookmarks, etc.) through a shared vocabulary. This enables cross-application tag searches and tag clouds.

Core classes:

• Content_Tagger -- The main API for tagging, untagging, searching, and building tag clouds.
• Content_Types_Manager / Content_Objects_Manager / Content_Users_Manager -- manage the type, object, and user registries that Content_Tagger depends on.

Horde applications do not call the HTTP endpoints directly. Instead each app defines a thin wrapper that extends Horde_Core_Tagger and declares its app name and supported object types:

class Nag_Tagger extends Horde_Core_Tagger
{
    protected $_app = 'nag';
    protected $_types = ['task'];
}

Horde_Core_Tagger obtains a Content_Tagger instance via the injector and delegates the heavy lifting. Apps that follow this pattern include Kronolith (events), Turba (contacts), Nag (tasks), Mnemo (notes), Trean (bookmarks), Ansel (photos/galleries), and Jonah (stories).

The most commonly used operations are tag(), untag(), replaceTags(), getTags(), getObjects(), and getTagCloud().

Content also exposes a set of PSR-15 request handlers mounted under the application's web root. All endpoints currently require a Horde session (default middleware stack).

PLANNED FEATURE: Allow making some endpoints public by opt-in.

Search or list tags. Returns all tags when called without parameters.

Most recently used tags.

Tag an object. Accepts POST or PUT.

Returns 204 No Content on success.

Remove a tag from an object. Accepts POST or DELETE.

Same parameters as /tag. Returns 204 No Content on success.