You will have to use the regular XML Reader. Point to the top tag in the XML (if you are using FME 2016 this will be displayed as a tree window, before that you have to get it using a XML editor).
Flatten all attributes but exclude the geometry object (that needs to be one attribute and not be flattened).
The use the GeometryReplacer to create a geometry from the GML geometry attribute.
It will be a lot of trying and re-trying but it can be done.
The XML reader will work if you are on FME 2015 or prior, but the easiest thing to do is download FME2016 and use the new IndoorGML reader.
The XML reader will work if you are on FME 2015 or prior, but the easiest thing to do is download FME2016 and use the new IndoorGML reader.
Did not know this. So use FME 2016 and disregard my answer!