Hello Michael,

Thanks a lot to looking at this already !
I didn't find any doc about that subject, however maybe I did something wrong on my side previously, but the ASCII version works too now (maybe by switching to .FBX 2013).
Here's a simple cube example where I did assign a custom 'id' and saved as .FBX 2013 ASCII. I can see in a text editor the 'LayerElementUserData', describe as such :


LayerElementUserData: 1 {
Version: 101
Name: "UserDataLayer1"
MappingInformationType: "ByPolygon"
ReferenceInformationType: "Direct"
UserDataId: 1
UserDataArray: {
UserDataType: "Integer"
UserDataName: "id"
UserData: *6 {
a: 0,1,2,3,4,5
}
}
}