Bitrix Framework - is a PHP-based platform for the creation and management of various projects (websites and corporate portals). Presently, the platform supports two proprietary cores: legacy and new one. Documentation on the legacy core can be found here.
Core D7 – is not just a refactoring, its a change in the approach to code writing. Developers must consider the gradual phasing out of legacy code with new methods: ultimately, the old API will become something of an adapter, used for compatibility only. And the complete programming logic with corresponding refactoring will migrate to the new core.
The present documentation is provided for reference only. Detailed description of operational principles for the new core are provided in the Bitrix Framework training course.
Attention: New core implements principles of OOD. Currently, however, the core D7 is in active development stage, so due caution must be exercised when handling methods inheritance. A situation can occur, when an abstract method can be be added to the basic class. Its recommended for the developers to not inherit methods but to incapsulate them instead, using more secure and flexible approach.