struct Node does not need first_child pointer when it is TextNode/CommentNodes/etc. as they are just terminals. Yet text node here <div>text</text> do

struct Node does not need first_child pointer when it is TextNode/CommentNodes/etc. as they are just terminals. Yet text node here <div>text</text> does not need next/previous pointers as it is lone child. In case of DOM tree children-vector case takes always less than "children-dl-list" case. With only one exception - element with single child node when size of memory needed is the same as in "children-dl-list".