diff --git a/builtins.go b/builtins.go
index 1281887..0f94d76 100644
--- a/builtins.go
+++ b/builtins.go
@@ -7,7 +7,13 @@ import (
 	"os"
 )
 
+// FALSE is a flag for, what else, false
 var FALSE = 0
+
+// TRUE is a flag for, what else, true.
+// It's -1 because historically, FORTHs would define TRUE as "all bits set to 1 in a cell",
+// and interpreting that literally flips the sign flag in a signed integer.
+// More generally, TRUE is defined as "not FALSE" for most purposes, and any non-zero integer will work.
 var TRUE = -1
 
 // Builtins is a handy holder for our various default words