M3 § Checkbox, Behaviour asks that from expanded (840px) related checkboxes be gathered into a contained region rather than left as one long column. That is a rule about the page around the control, not about the control, so it is written down rather than built: the component's header and its SKILL.md entry now say it, and the showcase lays a group out in an `expanded:grid-cols-2` card (plan step 24, audit docs/audits/m3-alignment/inputs.md § Missing). Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9