In addition to the generic FME feature attributes that FME Workbench adds to all features (see About Feature Type Attributes), this format also adds format-specific attributes (Format Attributes).
Special FME feature attributes are used to hold IDEX information. These attributes store values from specific sections of the IDEX file. Correspondingly, they enable the writer to write values to specific sections. User-defined attributes are contained in FME features and, when writing, are defined in the DEF lines.