"Member-of-groups" container
The "member-of-groups" container is a top-level config.txt file entry which can be used by any content type. This container was introduced in trainz-build 3.5 and is not valid in older-version Config.txt files.
The container holds a regular list of KIND Asset-group KUIDs. This asset will be considered as a member of each listed asset group.
If no entries are specified for a given "member-of-groups" container, or if the asset omits the "member-of-groups" container, then the simulator may specify some default asset groups based on the asset's Config.txt file. The exact behaviour may change between different versions of the simulator, however the current logic is described here.
The actual interpretation of what membership of a given asset-group means is documented here.
"member-of-groups" Example
The following is an example of a simple member-of-groups container. This example declares the asset as a member of the 'Bridge Spline Group' and the 'Road Spline Group' (not necessarily a sensible combination.)
member-of-groups { 0 <kuid:30501:100046> 1 <kuid:30501:100045> }