diff --git a/web/web_arg_utils.anubis b/web/web_arg_utils.anubis
index be6afed..8f351dc 100644
--- a/web/web_arg_utils.anubis
+++ b/web/web_arg_utils.anubis
@@ -360,6 +360,26 @@ public define Maybe(Bool)
 //      println("value = '"+value+"' result = "+to_String(return_v)+" success("+to_String(return_v)+")");
       success(return_v)
   }.
+
+public define Maybe(Bool)
+  get_tristate
+  (
+    List(Web_arg) lwa,
+    String        arg_name
+  ) =
+//  println("get_mb_Bool "+arg_name);
+  if web_arg_value(lwa, arg_name) is
+  {
+    not_found     then failure
+    found(value)  then 
+      if value = "checked"            then success(true)
+      else if value = "unchecked"     then success(false)
+      else if value = "intermediate"  then failure
+      else failure,
+//      println("value = '"+value+"' result = "+to_String(return_v)+" success("+to_String(return_v)+")");
+
+  }
+.
   
 public define Bool
   get_Bool
--
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