src/document/doc-utils.js/breakParentGroup
function breakParentGroup(groupStack) {
  if (groupStack.length > 0) {
    const parentGroup = getLast(groupStack);
    // Breaks are not propagated through conditional groups because
    // the user is expected to manually handle what breaks.
    if (!parentGroup.expandedStates && !parentGroup.break) {
      // An alternative truthy value allows to distinguish propagated group breaks
      // and not to print them as `group(..., { break: true })` in `--debug-print-doc`.
      parentGroup.break = "propagated";
    }
  }
  return null;
}