XSL Transformations that can be called with a CALL TRANSFORMATION statement must exist in the Repository as XSLT programs. XSLT programs are edited in the Transformation Editor, which can be accessed directly using transaction STRANS called up in the Object Navigator of the ABAP Workbench by choosing Edit Object → More → Transformation (or XSLTProgram before release 6.40 and XSLTransformation before release 6.20) and selecting XSLTProgram.
SAP delivers the identity transformation under the name ID. If you perform an identity transformation from XML to XML, the result is a copy of the source document. If you perform an identity transformation from ABAP to XML, this results in a canonical XML representation (asXML) of the ABAP data (explicit serialization). An identity transformation from XML to ABAP transforms a canonical XML representation to ABAP data (explicit deserialization).