"Elements that exist in the current head will be left along" s/along/alone/ I think two things could be clarified: the head tag can be anywhere? Some may assume they have to use a whole tag to get this behavior. Second, the matching/swapping relies on an exact textual match of each tag in head? As opposed to a structural match e.g. The order and whitespace of attributes matters. No need to answer me here but I feel like those are two immediate questions