VMS Help MMS, Description File, Dependency rules, User-defined Rules  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    You can define your own rules in a description file if MMS  does  not
    supply  a built-in rule that meets your needs.  Once you define a new
    rule, MMS uses  it  every  time  it  builds  your  system  with  that
    description file.

    Format:

      .SRC.TAR     [! comment]
              action line...     [! comment]

    .SRC is the source file type, and .TAR is the target file type.   The
    comment  is  a  string  of text that documents your rule.  The action
    lines specify the CLI commands that MMS should execute  to  update  a
    file  of  the  target  type from a file of the source type.  Both the
    source and target file types must appear in the  suffixes  precedence
    list.