/* ChangeType::PENDING and ChangeType::CANCELLED may be emitted from any thread; ChangeType::DONE always from GUI thread */
boost::signals2::signal<void (ChangeType, std::weak_ptr<Content>, int, bool)> Change;
/* ChangeType::PENDING and ChangeType::CANCELLED may be emitted from any thread; ChangeType::DONE always from GUI thread */
boost::signals2::signal<void (ChangeType, std::weak_ptr<Content>, int, bool)> Change;