n1 = spaces indented (The default is 5.)

    Specifies (like .INDENT) how many character positions to the
    right of the .LEFT MARGIN setting the first line of text will
    begin.

 -n1

    Specifies how many character positions to the left of the .LEFT
    MARGIN setting the first line of text will begin; -n1 cannot,
    however, cause the text to begin to the left of character
    position 0.

 n2 = vertical spacing (The default is 1.)

    Specifies (like .SKIP) the number of blank lines you want
    inserted before the paragraph. You get additional blank lines
    if the .SPACING value is greater than 1.

 -n2

    Specifies that the next line of text be pushed to within n2
    lines of the bottom of the current page by the insertion of
    blank lines. Every line but the last one retains the line spacing
    (.SPACING value) that follows it.

 n3 = test page lines (The default is 2.)

    Specifies (like .TEST PAGE) the number of lines of text required
    to be on one page. Unlike the .TEST PAGE command itself, n3 takes
    into account any blank lines that .SPACING routinely inserts
    after each line of text. If there is not enough room on the
    current page to accommodate that many lines, DSR puts the text
    on the next page. You can cancel this function by specifying 0
    for n3.