@mixin auto-numbers($numbered-element, $sep, $counter: item, $nested-parent: false ){
    $sel: ();
    @if $nested-parent {
        $sel: append($sel, unquote($nested-parent));

        #{$nested-parent}{
            list-style: none;
            margin-left: 0;
        }
    }
    $sel: append($sel, unquote('&'), comma);

    #{$sel}{
        counter-reset: #{$counter};
        > #{$numbered-element}{
            &:before{
                counter-increment: #{$counter};
                content: if($nested-parent, counters(#{$counter}, "#{$sep} ") "#{$sep} ", counter(#{$counter}) "#{$sep} ") ;
            }
        }
    }
}