The SET MARGINS command affects only the display of source lines.
    It does not affect the display of other debugger output, as from
    an EXAMINE command.

    The SET MARGINS command is useful for controlling the display
    of source code when, for example, the code is deeply indented
    or long lines wrap at the right margin. In such cases, you can
    set the left margin to eliminate indented space in the source
    display, and you can decrease the right margin setting (from its
    default value of 255) to truncate lines and prevent them from
    wrapping.

    The SET MARGINS command is useful mostly in line (noscreen) mode.
    In line mode, the SET MARGINS command affects the display of
    source lines resulting from a TYPE, EXAMINE/SOURCE, SEARCH, or
    STEP command, or when a breakpoint, tracepoint, or watchpoint is
    triggered.

    In screen mode, the SET MARGINS command has no effect on
    the display of source lines in a source display, such as the
    predefined display SRC. Therefore it does not affect the output
    of a TYPE or EXAMINE/SOURCE command, since that output is
    directed at a source display. The SET MARGINS command affects
    only the display of any source code that might appear in an
    output or DO display (for example, after a STEP command has
    been executed). However, such source-code display is normally
    suppressed if you enable screen mode by pressing PF1-PF3, because
    that sequence issues the SET STEP NOSOURCE command as well as SET
    MODE SCREEN to eliminate redundant source display.

    By default, the debugger displays a source line starting at
    character position 1 of the source line. This is actually
    character position 9 on your terminal screen. The first eight
    character positions on the screen are reserved for the line
    number and cannot be manipulated by the SET MARGINS command.

    If you specify a single number, the debugger sets the left margin
    to 1 and the right margin to the number specified.

    If you specify two numbers, separated with a colon, the debugger
    sets the left margin to the number on the left of the colon and
    the right margin to the number on the right.

    If you specify a single number followed by a colon, the debugger
    sets the left margin to that number and leaves the right margin
    unchanged.

    If you specify a colon followed by a single number, the debugger
    sets the right margin to that number and leaves the left margin
    unchanged.

    Related commands:

       SET STEP [NO]SOURCE
       SHOW MARGINS