eval.c:6186
static VALUE
rb_mod_private(argc, argv, module)
    int argc;
    VALUE *argv;
    VALUE module;
{
    secure_visibility(module);
    if (argc == 0) {
	SCOPE_SET(SCOPE_PRIVATE);
    }
    else {
	set_method_visibility(module, argc, argv, NOEX_PRIVATE);
    }
    return module;
}
