The (Bentley) MicroStation GeoGraphics Reader/Writer is nearly identical to the Intergraph MGE Reader/Writer.
The only difference is that by default, the Format Type Identifier (short name) for the MGE reader is MGE.
Refer to the chapter Intergraph MGE Reader/Writer for specific information about both the GG and MGE formats.
Overview
FME can read and write design files and their associated databases. This chapter assumes an operational knowledge of MicroStation GeoGraphics.