"Your data structure looks to me like it's roughly optimal for the case where the DOM tree is generated once and then is never or rarely modified" Check gmail

"Your data structure looks to me like it's roughly optimal for the case where the DOM tree is generated once and then is never or rarely modified" Check gmail for example. It has just one list - element that has 100 children. Other elements have from 0 to 10 children. And that 100 list is normally populated as a whole. "even one without any children, you have to allocate a new `vector`" You don't need to allocate anything if vector is empty ... Vectors's data buffer gets allocated only when you put something in the vector. At least in my case. So empty vector is just one pointer - nothing to write home about it. "every insertion, move or deletion in an arbitrary location requires updating the `node_index` of every sibling" On any DOM insertion you need to scan all siblings almost always anyway. For quite many reasons, e.g. to reset styles that could use `this ~ that` or something like `:nth-child(odd)`