Browser Architecture
├── User Interface
│   └── Address bar, buttons, bookmarks
├── Browser Engine
│   └── Coordinates rendering and browser processes
├── Rendering Engine (Blink/WebKit/Gecko)
│   ├── HTML Parser → DOM Tree
│   ├── CSS Parser → CSSOM
│   ├── Layout → Render Tree
│   └── Paint → Composite
├── JavaScript Engine (V8/SpiderMonkey/JSC)
│   ├── Parser → AST
│   ├── Interpreter → Bytecode
│   └── JIT Compiler → Machine Code
├── Networking
│   └── HTTP, WebSocket, DNS
├── Data Storage
│   └── Cookies, localStorage, IndexedDB
└── GPU Process
    └── Compositing, WebGL

Browser Request Lifecycle
1. URL Input
   └── Parse URL, check cache
2. DNS Lookup
   └── Browser cache → OS cache → DNS resolver
3. TCP Connection
   └── 3-way handshake (+ TLS for HTTPS)
4. HTTP Request
   └── Send request with headers
5. Server Processing
   └── Process request, generate response
6. HTTP Response
   └── Receive response, handle caching
7. Rendering
   └── Parse HTML → Build DOM → Layout → Paint
8. JavaScript Execution
   └── Parse → Compile → Execute

CORS Flow
1. Browser sends request with Origin header
2. Server responds with Access-Control-Allow-Origin
3. Browser allows or blocks based on response

Preflight (for non-simple requests):
1. Browser sends OPTIONS request
2. Server responds with allowed methods/headers
3. Browser sends actual request