Eclipse BIRT report files (report.rptdesign) are simply XML documents with a funny extension. The extension allows the Eclipse IDE to recognize the file as a BIRT report. The Pentaho BIRTReportComponent (org.pentaho.plugin.eclipsebirt.BIRTReportComponent) is capable of executing these reports, and producing output as HTML, PDF, FO, and FOP.
Eclipse BIRT parameters are defined in the report definition as Scalar Parameters. In BIRT a parameter must be added to a Data Set. This is done when creating a Data Set or while editing an existing Data Set. There is a "Parameters" section of the Data Set editor dialog which is where you will define your parameters. When defining the parameter the "Default Value" must follow the convention params[Reporting:"SOME_PARAMETER"]. The "SOME_PARAMETER" must match the name of a report parameter as defined in BIRT's Data Explorer "Report Parameters" section.
For the example above, with a report parameter named "REGION", the report parameter has been defined as shown below.