Method collapsing_header

src/python/lfs/py_ui.cpp:1462–1468

        pop_per_item_state();
    }
    bool PySubLayout::collapsing_header(const std::string& l, bool default_open) {
        advance_child();
        apply_state();
        auto r = parent_->collapsing_header(l, default_open);
        pop_per_item_state();
        return r;
    }
    bool PySubLayout::tree_node(const std::string& l) {
        advance_child();
        apply_state();