Library /sys$common/syshlp/helplib.hlb

 n

    Specifies the number of the character position of the left
    margin. For example, .LEFT MARGIN 0 sets the left margin just
    to the left of the first character position.

 +n

    Sets the left margin n character positions to the right of the
    current left margin.

 -n

    Sets the left margin n character positions to the left of the
    current left margin.