Frontend & browser·Rendering and the browser pipeline
you open the elements panel and the tree you see is not the HTML you wrote, because scripts changed it.
Document Object Model
Also calledDOM, document tree
The live tree of objects the browser builds from parsed HTML and exposes to JavaScript. It is the source of truth for what is on the page, not the HTML file, which is why 'view source' and the elements panel disagree on any page with scripts. Every DOM node carries substantial memory and every mutation can invalidate layout, so the tree's size is a performance number and not just a structural detail.