Library /sys$common/syshlp/lse$clihelp.hlb SET, LEFT_MARGIN, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 column-number
    Specifies the column for the left margin. The value must be
    greater than or equal to one and less than the value set for the
    right margin.

    If you specify the CONTEXT_DEPENDENT value as the column number,
    then LSE uses the indentation of the current line to determine
    the left margin when you use the /WRAP qualifier. When you use the
    FILL command, LSE uses the indentation of the first line of each
    selected paragraph to determine the left margin.