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]

1  –  Parameters

 n

    The subpage letter that will be appended to the number of the
    next page. You can specify the letter itself (A) or you can
    specify a number corresponding (in order) to the letter that
    the subpage will have. For example, 1=A, 26=Z, 27=AA, 28=AB.

 +n

    Specifies how many alphabetically ordered letters past the
    current subpage letter the next subpage letter will be. For
    example, if the current subpage is page 3-12E, then .NUMBER
    SUBPAGE +2 will cause the next subpage to be numbered 3-12G.

 -n

    Specifies how many alphabetically ordered letters before the
    current subpage letter the next subpage letter will be.

2  –  Default

    Sequential uppercase lettering, beginning with A.