gistfile1.txt

@h|50-[#something]-10-(.value:first)-20-(.probably-many)-| gap(10) outer-gap(15)
 
#something, .value:first, .probably-many {
  // default gap
  [gap] == 10
  
  // gap for specific element
  &:matches(.value:first) {
    [gap] == 20
  }
  &:first {
    left == 50
  }
  &:last {
    right == 15
  }

  &:next {
    left == ::previous[right] + ::previous[gap]
  }
}