rscope uses seq_trace for global variables scoped within the
execution of a single request.
At this point you might say: "Oh, the horror! What kind of twisted use case could there be for this?" It's very easy, you can set a variable early in the execution of the request (for example "identity" can be set during the HTTP handling) and later used when collecting metrics or logging.
It can work something like this:
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In your HTTP handler, call request:identity/1 to identify the request as "fetch document", "update invoice", etc.
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In your business logic in another process, call rscope:identity/0 to retrieve the identity and use it for collecting metrics or logging.
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When the request is complete, ie. you are back in the HTTP handler returning the response, call rscope:request_complete/0 to clean up the cached request identity.