Spell a reference path as arm.isRefPath, and say where each tail's head is held

format.go

@@ -303,8 +303,8 @@ func checkNoRepeatedArm(body string, names []string) error {
 
 // arm is one alternative of a {a|b} token or one operand, split into the head
 // `template.head` resolves and the tail of a dotted path into it. A non-empty tail
-// is what makes the arm a held draw: its head is drawn once per expansion (see
-// compileOps).
+// makes the arm a held draw: a reference path's for the render, any other for the
+// expansion.
 type arm struct {
 	spelling    string // as written, for messages
 	head        string
@@ -314,6 +314,10 @@ type arm struct {
 	path        string   // head and tail, the one path every way of writing this read shares
 }
 
+func (a arm) isRefPath() bool {
+	return isRef(a.head) && len(a.tail) > 0
+}
+
 // splitArm splits one name into head and tail. refs maps a reference to what
 // linkRefs resolved it to; before linking, a reference is whole.
 func splitArm(name string, refs map[string]refBinding) arm {
@@ -397,7 +401,7 @@ type firstReach struct {
 }
 
 func (c *formatOps) holdName(a arm, label string) {
-	if isRef(a.head) && len(a.tail) > 0 {
+	if a.isRefPath() {
 		return
 	}
 	if c.held == nil {