diff --git a/src/evalvars.c b/src/evalvars.c
index 0b51ce1..71cab0a 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -2953,6 +2953,7 @@
 	    {
 		if (rettv != NULL)
 		{
+		    // special value that is used in handle_subscript()
 		    rettv->v_type = VAR_ANY;
 		    rettv->vval.v_number = sid != 0 ? sid : import->imp_sid;
 		}