Sandboxing
Sandboxing in session replay is the isolation of the rebuilt page inside a restricted iframe so that nothing from the recorded session can execute during playback. Replay must show exactly what happened while guaranteeing that scripts, form submissions, and navigation from the recorded page stay inert.
How it works
The replayer renders the deserialized DOM into an iframe with the sandbox attribute, which blocks script execution, and the rebuild step additionally neutralizes script contents and event handlers. The sandbox documentation explains this browser security boundary. Interactions in a replay are simulated visually (a synthetic cursor, highlighted clicks) rather than dispatched as real events. This matters because recordings routinely contain third-party markup: a recorded page carrying a malicious script must be safe to replay in an analyst's browser and in your admin panel.
Where you encounter it
Inside every replayer, and in embedding decisions: when replay is embedded into another product, the sandbox is what makes showing user-generated page content in your own UI defensible.