As a part of the enhancement concept, it is possible to enhance ABAP source code without changing the actual code, simply by adding enhancements.
Although source code plug-ins are displayed in the same source code as the respective enhancement options, the plug-ins are stored in other include programs managed by the Enhancement Builder:
The enhancement options in ABAP source code can be explicit and implicit:
A source code plug-in defined between ENHANCEMENT - ENDENHANCEMENT can be enhanced by additional source code plug-ins. This means that the ENHANCEMENT-POINT and ENHANCEMENT-SECTION statements can be listed in a source code plug-in. In addition, implicit enhancement options are now available before the first and after the last line of a source text plug-in (after ENHANCEMENT and before ENDENHANCEMENT).
More information about the usage of source code enhancements: