The bar commands control the insertion of vertical bars (|) at
    the beginning of lines of text. The bars (usually called change
    bars) are normally inserted to indicate where changes in text
    have occurred since the previous edition of a document. You can
    specify a character other than the default character (vertical
    bars) to indicate changes by using the /CHANGE_BAR qualifier to
    the RUNOFF command line.

    Formats

      .ENABLE BAR

      .DISABLE BAR

      .BEGIN BAR

      .END BAR

    Abreviated formats

      .EBB

      .DBB

      .BB

      .EB