The .SUBPAGE command begins a new page and a new format for page
    numbering. It numbers the new page by keeping the previous page
    number and appending the letter A to it. For example, if the
    previous page is 10, the first subpage is 10A and the next page
    becomes 10B unless you enter an .END SUBPAGE command. (See also
    .NUMBER SUBPAGE, .DISPLAY SUBPAGE, .HEADERS ON, .LAYOUT, and
    .PAGE.)

    The .END SUBPAGE command begins a new page and goes back to
    normal page numbering. If you enter the .END SUBPAGE command
    on page 2-8D, for example, the next page would be numbered 2-9.

    Formats

      .SUBPAGE

      .END SUBPAGE

    Abreviated formats

      .SPG

      .ES