Offer the reference hint only where it would render the same value, and name the guard set in the help

builtins.go

@@ -133,7 +133,7 @@ func transformArg(fields map[string]node, a []string) error {
 		_, _, err := refShape(leaf)
 		return err
 	}
-	return checkArm(leaf, fields)
+	return checkArm(leaf, fields, false)
 }
 
 func transformOperand(a []string) []string {

cmd/fejkdata/main.go

@@ -31,7 +31,8 @@ An argument containing a { token, or a JSON object, array or string, is a
 template; any other argument is a path (a path never contains a brace, a bracket
 or a quote). Templates reach the data by reference from the root —
 {/sv_SE.person.last} — whether the data is shipped or layered with --data-path. An
-argument carrying one of those characters but no valid JSON names neither.
+argument carrying a bracket, a closing brace or a quote but no valid JSON names
+neither.
 
   -d, --data-path D      a data directory to layer over the shipped data (repeatable; last wins on a clash)
   -h, --help             print this help, then exit

template.go

@@ -140,7 +140,7 @@ func checkTokens(format string, fields map[string]node) error {
 				}
 				continue // its target is checked at New (see linkRefs)
 			}
-			if err := checkArm(name, fields); err != nil {
+			if err := checkArm(name, fields, len(names) == 1); err != nil {
 				return fmt.Errorf("token {%s}: %w", t.body, err)
 			}
 		}
@@ -151,7 +151,9 @@ func checkTokens(format string, fields map[string]node) error {
 }
 
 // checkArm validates one sibling name or path against a template's fields.
-func checkArm(name string, fields map[string]node) error {
+// wholeToken says the name is the token's entire body, so {/name} would render
+// the same value and can be offered as the reference spelling.
+func checkArm(name string, fields map[string]node, wholeToken bool) error {
 	a := splitArm(name, nil)
 	if err := checkSegments(a); err != nil {
 		return err
@@ -166,7 +168,7 @@ func checkArm(name string, fields map[string]node) error {
 		}
 		if len(fields) == 0 {
 			hint := ""
-			if hintableRef(name) {
+			if wholeToken && hintableRef(name) {
 				hint = fmt.Sprintf(" — write {/%s} to reference the data", name)
 			}
 			return fmt.Errorf("no field %q; a token names a sibling field, and this template has none%s", a.key, hint)