[mtdowling]

Smithy is very focused on codegen, so the model is highly normalized. So for example, defining a list of something needs to be done using a `list` shape. This kind of list is something you'd see directly serialized and sent over the wire. For example:

list Messages { member: Messages }

Then you can reference Messages from other places in the model, like from a structure:

structure Something { messages: Messages }

In contrast, the `[City]` syntax is used in other places in the IDL to define a relationship to a shape. This isn't something that gets sent over the wire, it's just used to form essentially a relationship in the service graph from a service to resources, a resource to operations, an operation to errors, etc. For example:

service Weather { resources: [City, Sensors] }