diff --git a/src/tofrom_string.hpp b/src/tofrom_string.hpp
index f3f5b36b..63a778d5 100644
--- a/src/tofrom_string.hpp
+++ b/src/tofrom_string.hpp
@@ -26,4 +26,5 @@ class ToFromString
 public:
   virtual std::string to_string() const = 0;
   virtual int from_string(const std::string_view) = 0;
+  bool display = false;
 };