Keep the transform's arity inside its operand func, skip calls in compileWhole's column check, and file the two tokens for renaming

table.go

@@ -329,9 +329,12 @@ func (t *table) compileWhole(format string) error {
 		return err
 	}
 	for _, tok := range toks {
+		if tok.kind != 'f' {
+			continue
+		}
 		for _, name := range tok.names {
 			a := splitArm(name, nil)
-			if _, ok := t.col[a.key]; tok.kind == 'f' && !ok && !isRef(a.key) && a.key != "" {
+			if _, ok := t.col[a.key]; !ok && !isRef(a.key) && a.key != "" {
 				return fmt.Errorf("format names no column %q of %s; the columns are %v", a.key, t.file, t.columns)
 			}
 		}

template.go

@@ -265,10 +265,10 @@ func hintableRef(name string) bool {
 }
 
 // builtinOperands lists the fields a call reads as operands, empty for a builtin that
-// reads none, or a call checkFunc refuses.
+// reads none or is unknown.
 func builtinOperands(name string, args []string) []string {
 	b, known := builtins[name]
-	if !known || b.operands == nil || (b.arity >= 0 && len(args) != b.arity) {
+	if !known || b.operands == nil {
 		return nil
 	}
 	return b.operands(args)

todo.md

@@ -37,7 +37,8 @@ This round, in order:
 - Split `drawCheck.reads`'s six-term condition into named predicates.
 - Rename what names two things: `template.go` holds the token grammar while `template`
   is `node.go`'s type and `Template` `inline.go`'s; `kind` `'b'` is a brace body in
-  `ftoken` and a builtin in `op`; `drawAt.alt` holds the rows
+  `ftoken` and a builtin in `formatToken` and `op`; `tokens` is a template's parsed format
+  and a table's cell templates; `drawAt.alt` holds the rows
   a walk entered.
 - Run the nine-seat panel again and file what it names here.
 

transform.go

@@ -45,6 +45,9 @@ func transformArg(fields map[string]node, a []string) error {
 	return checkArm(leaf, fields, false)
 }
 func transformOperand(a []string) []string {
+	if len(a) != 1 {
+		return nil
+	}
 	leaf, _, err := unwrapTransform(a[0])
 	if err != nil {
 		return nil