Answer architecture round 2: refuse by default where a builtin's operand can be a reference, test the flag against each operand grammar, drop a duplicate test, rename allNeverNumeric, rewrap Computation, and order item 91 after item 4

format.go

@@ -133,9 +133,9 @@ type builtin struct {
 	// operands names the fields the call reads, which expand renders for it; nil
 	// for a builtin that reads none.
 	operands func(args []string) []string
-	// refOperands says an operand may be a reference, so a name read once there has the bare
-	// reference as a second spelling.
-	refOperands bool
+	// noRefOperands says no operand can be a reference, so a name read once there has no
+	// second spelling.
+	noRefOperands bool
 	// proveNumber bounds the number a call's text reads as, token its body, and says which
 	// datatypes that text is not; set it where every render reads as a finite number, which
 	// makes the call a calc operand, and leave it nil otherwise.
@@ -281,7 +281,7 @@ func checkReads(t formatToken, fields map[string]node, operands bool) ([]unbound
 			return nil, err
 		}
 		a := splitArm(name, nil)
-		unbound = append(unbound, unboundRead{head: a.head, tail: joinSegments(a.tail), body: t.body, operand: operands, noRef: operands && !builtins[t.fn].refOperands, err: err})
+		unbound = append(unbound, unboundRead{head: a.head, tail: joinSegments(a.tail), body: t.body, operand: operands, noRef: operands && builtins[t.fn].noRefOperands, err: err})
 	}
 	return unbound, nil
 }