Externalizers are object factories that use definitions in external files to initialize defined objects. This enables you to configure and customize these defined objects (or implement new ones) using the CHA Editor or something as simple as a basic text editor. The externalizer creates a structure of tags in memory, which it uses to store object definitions, from the tags in the generic file.

At runtime, an externalizer instantiates an object and uses the object's initializeFromTag method to initialize the object with specified values. The externalizer obtains the values from the object's definition in memory. An attribute called externalizer in the root class for each entity contains a reference to the entity's externalizer.

In the application presentation layer, the basic entities of the toolkit such as data, formats, services, contexts, types, processors, and views each have an externalizer and a generic XML file that contains tags. In the application logic layer, processors and views do not exist and consequently there are no externalizers for them.