YAy PEG: Fix grammar rule `ns_plain_first`
@@ -791,7 +791,7 @@ struct nb_single_multi_line : seq<nb_ns_single_in_line, sor<s_single_next_line,
// [126]
struct ns_plain_safe;
-struct ns_plain_first : sor<seq<not_at<c_indicator>, ns_char>, seq<one<'?', ':', '-'>, ns_plain_safe>>
+struct ns_plain_first : sor<seq<not_at<c_indicator>, ns_char>, seq<one<'?', ':', '-'>, at<ns_plain_safe>>>
{
};
