Combined +span() and +nested() for Susy. Using custom mixin with extended functionality instead of +span()

susy_span_nested.sass

// "/test/scss/ag.sass"

// ...

// Complex AG tests
// ----------------

=col($params)
  +span($params)
  @if nth($params, length($params)) == container
    +nested($params)
      @content

=ag-test($class)
  .#{$class}
    +container
    +leader(0.5)
    +trailer(0.5)
    > .size1of5
      min-height: rhythm(10)
      &:first-of-type
        +col(first 2)
      ~ .size1of5
        +col(last 2)
    > .size3of5
      +col(6 at 3 container)
        > .size1of2
          &:first-child
            +col(first 3)
          + .size1of2
            +col(last 3)
        > .full
          clear: both
          background: none
        .full
          .size1of3
            +col(first 2)
            min-height: rhythm(6.5)
          .size2of3
            +col(last 4 container)
              .size1of2
                &:first-child
                  +col(first 2)
                + .size1of2
                  +col(last 2)
          .full
            clear: both
    .gallery
      div
        +gallery(2)

// ...