Notes on session IDs and flagfall

This import format supports importing usage for long-held sessions across multiple files. This is useful when importing usage data for DSL subscriptions where a session may span days or weeks, potentially across rating periods.

When a session ID is provided, Smile groups the usage together and treats it as a single session. This allows session limits to affect rating, shaping and other session-related behaviours without needing to wait until the session has ended, and permits rating to be performed as the usage is logged rather than at the end of the session.