| Database abstraction layer | Allow the use of different database servers using the same code base. |
| Extra blogapi updates for 5.x | |
| Extra system updates for 5.x | |
| File interface | Common file handling functions. |
| Form generation | Functions to enable the processing and display of HTML forms. |
| Formatting | Functions to format numbers, strings, dates, etc. |
| Hook implementations for user-created content types. | |
| Hooks | Allow modules to interact with the Drupal core. |
| Input validation | Functions to validate user input. |
| Menu system | Define the navigation menus, and route page requests to code based on URLs. |
| Node access rights | The node access system determines who can do what to which nodes. |
| Search interface | The Drupal search interface manages a global search mechanism. |
| System updates from 4.7 to 5.0 | |
| System updates from 5.0 to x.x | @todo Start this series of updates at 2000. |
| Themeable functions | Functions that display HTML, and which can be customized by themes. |