diff --git a/formatter.go b/formatter.go
index 08f4110..d00fb8d 100644
--- a/formatter.go
+++ b/formatter.go
@@ -9,6 +9,10 @@ type FmtOpt uint16
 const (
 	TTY FmtOpt = 1 << iota
 	MultiLine
+	Base2
+	Base8
+	Base10
+	Base16
 )
 
 type Formatter interface {