How to write custom Solr plugin that can be called core container level instead of core level

[gnandre]

e.g. /solr/admin/cores request works without specifying specific core in
the request.

I took a look at the code of such request handlers (e.g. LoggingHandler)
but they simply extend to RequestHandlerBase just like any other core-level
request handler. What makes them special so that they do not require core
context?