Administration > Environment Variables > APTENTPATH — Specifying a Path for User-Defined Entities
  
APTENTPATH — Specifying a Path for User-Defined Entities
Specifies the default paths for the set entitypath option. That option sets the list of path names to directories that ArbortextEditor uses to locate entities that are not specified as absolute path names and not found in the document type directory and document cache directory. The default is Arbortext-path\entities.
The path can also be set in the File Locations category of the Tools > Preferences dialog box.
There are two symbolic parameters (%H and %D) that may be specified as part of the search path.
If you want to make entity files automatically accessible, use the Arbortext-path\custom\entities directory to load them automatically upon startup.