VMS Help MERGE, Specification File Qualifiers, /PAD, Full Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Use the /PAD qualifier to specify a pad character when comparing
    strings of unequal length or when reformatting records. By
    default, Sort uses the null character for padding, ensuring
    conformity with the previous versions. Double characters that
    can be defined as single characters ("ch" > "c") cannot be used
    as pad characters.