The Creative Suite Host Adapter libraries, delivered with CS Extension Builder 1.5, enable deeper integration with Photoshop, Illustrator, InDesign and InCopy Creative Suite applications than is possible through scripting with the Creative Suite Actionscript Wrapper (CSAW) libraries. For example the InDesign Host Adapter library supports the listening of ExtendScript scripting events within Actionscript and the retrieval and setting of XMP Metadata through a native C++ plugin.
Therefore if you are developing a workflow that requires the updating and/or retrieval of XMP metadata from an InDesign document or InCopy story, you will want to utilise the InDesign Host Adapter library.
Unfortunately, the current delivered InDesign Host Adapter in CS Extension Builder 1.5 is only compatible with InDesign CS5 and the 7.5.0 release on Mac OS. To support development for InDesign CS5.5 (including the 7.5.1 update) on Mac OS you will need to download the updated version located here.
For further information about the Host Adapter libraries please refer to:
CS Extension Builder help documentation.