Contained resources in StructureDefinitions?

[costateixeira]

I noticed a few contained resources in the profiles. I am not sure what this means.
The normal way to declare that a system (not a profile) supports search parameters, for example, is to put them in q CapabilityStatement.
Some of the search parameters seem to be repeated from the core specification, so why include them at all?

In short:

1. I don't see a reason why Search parameters are being redefined
2. Contained resources in a StructureDefinition is unusual/unclear to me - what the purpose, how it is expected to render, to work, etc