Child elements

Not everyone knows that any object in RW can have an unlimited number of child objects. These are simply other objects (more specifically, blueprints from a restricted subset of all the available ones).

Uses include:

• Signal panels attached to a post (which acts as the main element, but it could be the other way around just as well).
• Plates and other supplements attached to rolling stock (or station buildings).
• Freight items (called FreightAnim in MSTS)
• Lamps (tail lamps, head lamps)
  
• Sounds
• People (staff, passengers)
• Editor-only objects to show information or a bounding box to the routebuilder without disturbing the appearance in the game. Thanks Rail Similarity.
  

There are four ways to attach a child to a parent.

1. The official way. You have the source of both parent and child. You start the Asset Editor to show the parent and interactively position the child with the mouse.
2. The hacker version of (1). You add the reference to the child by editing the XML file which is the blueprint. This saves you the hassle of using the Asset Editor and often you will know the exact location from your documentation on the model (or by clicking on some vertex in the model in your 3D modelling programme). As long as you do not want rotation, this method can save time and nerves. See here for details.
3. The unofficial way. You do not own the sources of parent and child and still want to combine them, which is perfectly reasonable in a wide range of cases from the above list. You convert the BIN file of the parent to XML and add the reference there. Don't forget to convert the XML file back to BIN. See here for details.
4. You use RW Tools to do (3) in a user-friendly way.