Type Alias StreamingPosture

StreamingPosture: "grounded" | "roaming" | "consuming" | "motionless"

Streaming posture of an expression

grounded: Expression accesses nodes within a bounded region (streamable)
roaming: Expression can access any part of the document (not streamable)
consuming: Expression must buffer its input (limited streaming)
motionless: Expression doesn't navigate from context (fully streamable)