The .NUMBER SUBPAGE command allows you to specify the beginning
    of a new sequence of subpage numbers, for example, 1-16A, 1-16B,
    1-16C, and so on. This command affects only the letters that the
    .SUBPAGE command appends to the normally numeric page number.
    .NUMBER SUBPAGE takes effect on the next page. (See also .SUBPAGE
    and .DISPLAY SUBPAGE.)

    Format

      .NUMBER SUBPAGE  [[+/-]n]

    Abreviated format

      .NMSPG  [[+/-]n]