ContentImporter Generic Class
Importers, either provided by the framework or written by a developer, must derive from ContentImporter, as well as being marked with a ContentImporterAttribute.
An importer should produce results in the standard intermediate object model. If an asset has information not supported by the object model, the importer should output it as opaque data (key/value attributes attached to the relevant object). By following this procedure, a content pipeline can access specialized digital content creation (DCC) tool information, even when that information has not been fully standardized into the official object model.
You can also design custom importers that accept and import types containing specific third-party extensions to the object model.
Assembly: Microsoft.Xna.Framework.Content.Pipeline (in microsoft.xna.framework.content.pipeline.dll)