What type of messages can be used in services?(existing and custom)

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Hello!

I was just curious about what kind of messages I can transmit over services and topics. Is there a list available somewhere which I can refer to for this? I know that simple messages can be of the following types

1)a built-in type, such as "float32 pan" or "string name"

2)names of Message descriptions defined on their own, such as "geometry_msgs/PoseStamped"

3)fixed- or variable-length arrays (lists) of the above, such as "float32[] ranges" or "Point32[10] points"

4)the special Header type, which maps to std_msgs/Header

Also, what if I want to pass my own class instance as a message? What do I need to do that?

All help is greatly appreciated. Thanks!