.SHOW and .NOSHOW specify listing control options in the source
    text of a program. You can use .SHOW and .NOSHOW with or without
    an argument list.

    .SHOW and .NOSHOW control the listing of the source lines that
    are in conditional assembly blocks (see the description of .IF),
    macros, and repeat blocks. When you use them without arguments,
    these directives alter the listing level count. The listing level
    count is initialized to 0. Each time .SHOW appears in a program,
    the listing level count is incremented; Each time .NOSHOW appears
    in a program, the listing level count is decremented.

    When the listing level count is negative, the listing is
    suppressed unless the line contains an error. Conversely, when
    the listing level count is positive, the listing is generated.
    When the count is 0, the line is either listed or suppressed,
    depending on the value of the listing control symbolic arguments.