void mobi_free_opf_guide(OPFguide *guide) {
    if (guide) {
        mobi_free_opf_struct_3el(guide->reference, type, title, href);
        free(guide);
    }
}
void mobi_free_opf_guide(OPFguide *guide) {
    if (guide) {
        mobi_free_opf_struct_3el(guide->reference, type, title, href);
        free(guide);
    }
}