diff --git a/docs/authoring-guide.md b/docs/authoring-guide.md
index 94bb315..82975b7 100644
--- a/docs/authoring-guide.md
+++ b/docs/authoring-guide.md
@@ -344,6 +344,14 @@ separate in-session bool — `bars_since_open` alone is the contract. DST is
 handled by `chrono-tz`, so the same local minute reads the same index in
 summer (CEST) and winter (CET).
 
+The index is derived from the clock (`ctx.now()`), never counted from trigger
+firings — so the trigger's cadence only sets how *often* the node emits, not
+what it emits. Feeding a denser stream (e.g. a raw m1 `price`) is equally
+valid: the node fires once per input tick and reports the same
+`period_minutes`-bar index throughout that bar. The once-per-bar wiring above
+is the convention when you want exactly one emission per completed bar; it is
+not a correctness requirement.
+
 Wire it like any node —
 `{"op":"add","type":"SessionFrankfurt","bind":{"period_minutes":{"I64":15}}}`,
 feed its `trigger` from a once-per-bar stream, and read `bars_since_open`.