public String remove(Object key) {
        Layout l = layout.get(key);
        if (l != null) {
            l.clearValue();
        }
        return storage.remove(key);
    }

    @Override
    public void clear() {
        for (Layout l : layout.values()) {
            l.clearValue();
        }
        storage.clear();
    }

    /**
     * Return the comment header.
     *