Figure 5.5. expander

The expander statement (optional) is used to specify domain specific language (DSL) configurations (which are normally stored in a separate file). This provides clues to the parser as how to understand what you are raving on about in your rules. It is important to note that in Drools 4.0 (that is different from Drools 3.x) the expander declaration is mandatory for the tools to provide you context assist and avoiding error reporting, but the API allows the program to apply DSL templates, even if the expanders are not declared in the source file.