The first non-comment, non-empty, line in a mapfile is expected to be a mapfile version declaration. This declaration establishes the version of the mapfile language used by the remainder of the file. The mapfile language documented in this manual is version 2.
A mapfile that does not begin with a version declaration is assumed to be written in the original mapfile language defined for System V Release 4 Unix (SVR4) by AT&T. The link-editor retains the ability to process such mapfiles. Their syntax is documented in Appendix B, System V Release 4 (Version 1) Mapfiles.