Entity Tracking API

This module provides an API to track entities. When working with complex content, it is important for editors to get information about entities they are working with. Some examples of this are:

• Track complex relations between entities (how/where is an entity being used).
• Track misconfigurations (keep track of external IDs in content to get notified when external APIs remove the referenced ID).
• Track (internal/external) links in content (get notified when an internal or external link no longer exists).

How does it work?
To use the API, modules can simply provide a custom entity type and 1 or more tracking plugins. A tracking plugin can "subscribe" to 1 or more field types. When content is being saved, all tracking plugins are called for each field of the type they are subscribed to. The plugin can fetch the information it needs from the field data, and store the information it wants to track in the custom entity.

The tracked information can be displayed for anyone that needs the information. An example of this would be the Entity Usage module, which provides a tab for entities to show how/where the entity is being used by other entities.