DOM

The DOM (Document Object Model) is the in-memory representation of an HTML or XML document that a browser constructs after parsing the markup. It is not the document itself; it is the browser's interpretation of the document — a tree of nodes that can be manipulated by scripts, styled by CSS, and traversed by accessibility tools. The DOM transforms a static markup file into a dynamic runtime object, collapsing the distinction between document and application. This is the technical mechanism that makes the modern web possible, but it is also the architectural decision that made web documents as unstable as running software: a DOM can be destroyed and rebuilt by any script, and the document you see is never the document that was written.