The CORE HL7 Viewer comes with ANSI definitions for HL7 versions 2.2, 2.3, 2.4, 2.5.1 and 2.6. Access to view these HL7 Definitions or create new ones is accomplished in the Viewer Settings section 3.
Installed HL7 Definitions
Use the Current HL7 Definition section of the Viewer Settings to manage your CORE HL7 Definitions. You can see further options when you RIGHT CLICK on a HL7 Definition in the list (see below).
RIGHT Click a HL7 Definition
Editing a Custom HL7 Definition