Cover the ancestor clash and name what drawCheck compares by

drawfence.go

@@ -226,7 +226,8 @@ func newDrawWalk() *drawWalk {
 
 // walk follows what rendering n renders. A repeat renders over draws of its own, so the walk stops
 // there. A cell whose row the pins keep out has no case: a pinned table renders its pinned row
-// alone, so that cell never renders on this route.
+// alone and an unpinned one draws a row inside its nearest pinned ancestor's, so that cell never
+// renders on this route.
 func (w *drawWalk) walk(n node, at drawAt) {
 	v := nodeVisit{n, at.group, at.rowsKey()}
 	if w.seen[v] {

family.go

@@ -102,10 +102,10 @@ func checkFamilies(reads []pathRead) error {
 	return replayPairs(reads)
 }
 
-// replayPairs replays every two reads of one draw group that can render together into
-// one draws, the earlier read first. Pairs find every conflict a full replay would: a
-// read pins a row's ancestors with it, and clash judges a row against one pinned table,
-// so a conflict is between two reads' pins and a third read adds nothing to it.
+// replayPairs replays every two reads that can render together into one draws, the earlier
+// read first. Pairs find every conflict a full replay would: clash judges a row against one
+// pinned table, and the read that pinned it holds that pin itself, since a read's pins carry
+// its rows' ancestors, so the pair of those two reads clashes the same way.
 func replayPairs(reads []pathRead) error {
 	for i, r := range reads {
 		if r.tr == nil {

holdfence.go

@@ -18,7 +18,7 @@ func heldCheck(path string, n node) error {
 	readers := boundReaders(t.ops, t.bound)
 	for _, head := range heldHeads(t) {
 		if _, isPath := t.bound[head]; isPath && isRef(head) {
-			continue // held for the render: drawCheck compares it across the render and its groups
+			continue // held for the render: drawCheck compares every read of it, by path, across the render and its groups
 		}
 		if err := checkHeadHeld(t, head, readers); err != nil {
 			return fmt.Errorf("%s: %w", path, err)