child_begin
for (node::child_iterator i=n->child_begin(), e=n->child_end() ; i!=e ;
if (n->child_begin() == n->child_end())
std::sort(child_begin(), child_end(), cmp_children);
if (local_fixups->child_begin() != local_fixups->child_end())
child_iterator begin() { return n.child_begin(); }