Inheritance for documentclass options is not correct. See ``\documentclass[DIV=12]{ic-book}``. Proper order in cls needs to be: 1. ``\keys_define:nn {l3icbook} { ... DIV ... }`` 2. ``\DeclareUnknownKeyHandler`` 3. ``\ProcessKeysOptions{l3icbook}`` to use relevant options and set initials 4. ``\ProcessKeyOptions`` to handle remaining options and send them to scrbook. 5. Remove ``\PassOptionsToPackage`` for setting default Like this: ~~~tex \keys_define:nn {l3icbook} { DIV .code:n = {\PassOptionsToClass{DIV = #1}{\g_icbook__base_class_str}}, DIV .initial:n = 11, DIV .value_required:n = true } ~~~