Behavioral substrate
A behavioral substrate is the foundational data layer that captures how interfaces are used, by humans or by agents, in a form other systems build on. The term positions DOM-level session data as infrastructure: replay tools, analytics, AI analysis, and agent training all consume the same underlying event stream rather than each capturing reality separately.
How it works
The idea comes from the shape of rrweb data. The recorder starts with a serialized DOM snapshot and then emits timestamped events for later changes and interactions. The rrweb project structure and replay design notes document that model. Because the result is structured, one recording can support playback, derived product analytics, debugging, and carefully governed model inputs. Each downstream use still needs its own processing and privacy rules. "Behavioral substrate" is rrweb's name for treating this reusable event layer as infrastructure, not an established browser standard.
Where you encounter it
Architecture discussions about where behavioral data capture belongs in a stack, and rrweb's own framing of the record layer.