This chapter describes TYPO3 extensions from the developer's point of view. After reading this chapter, the reader will have basic knowledge of extension structure, files, and how extensions interact with TYPO3. This knowledge is necessary for extension planning and implementation.
All TYPO3 extensions are classified into several predefined categories. These categories do not actually differentiate the extensions. They are more like hints for users about extension functionality. Often, it is difficult for the developer to decide which category an extension should belong to. The same extension can provide PHP code that fits into many categories. An extension can contain Frontend (FE) plugins, Backend (BE) modules, static data, and services, all at once. While it is not always the best solution to make such a monster extension, sometimes it is necessary. In this case, the extension author should choose the category that best fits...