Experienced TYPO3 developers consult the API Documentation on a daily basis. As a courtesy, we've provided links to the core documentation below.

• div: general purpose functions (frontend and backend)
• extmgm: extension management functions
• befunc: class containing standard backend functions
• db: database abstraction layer (frontend and backend)
• template: backend templating path
• lang: backend localization class
• pibase: base class for frontend plugins
• content: class containing the main TypoScript rendering functionality
• TSREF: in-depth TypoScript documentation

As any seasoned TYPO3 developer can tell you, automatically generated documentation from the TYPO3 codebase is an essential part of extension development. TYPO3.org hosts API documentation for version 4.0.0, which is helpful. At Cast Iron Coding, we often find ourselves needed to dig through the core TYPO3 code while developing extensions, and we do so using our own in-house versions of the API docs generated from each major TYPO3 release since 4.0.0, which is when the core team began carefully documenting the source.

• TYPO3 4.0.7 API Documentation
• TYPO3 4.1.2 API Documentation
• TYPO3 4.2.0alpha1 API Documentation

If you have any suggestions as to how we can improve this documentation, please don't hesitate to let us know.