Browser Rendering Pipeline: Web layout engines parse HTML tokens into the Document Object Model (DOM) tree, evaluate CSS rules to generate the CSSOM, compute the Render Tree, execute layout/reflow, and paint raster pixels.
Event Loop & V8 Engine: JavaScript executes single-threaded on the event loop with call stack, microtask queue (Promises), and macrotask queue (setTimeout, DOM events).
Iframe Sandboxing: The right stage hosts an isolated document context that receives live DOM mutations via standard HTML5 document write streams.
Operating Instructions: Write standard HTML, CSS styles, and JavaScript scripts in the editor on the left; the visual stage updates live on key input.