not sure if this is correct - its ok to not check the bounds of the dates as thats' already handled by the other validation, but from the way I read the rule, I think these should be the conditions: 

```ruby

    if child.end_date.blank? || parent.end_date.blank?
      parent.start_date =< child.start_date
    else
      parent.start_date =< child.start_date && parent.end_date >= child.end_date
    end

```

By span, they mean the parent start date must be before or equal the child and the end date must be after or equal the child