universal-browser-device-supportlisted

# Universal Browser & Device Support ## Why this exists "It works on my machine" is the single most expensive lie in frontend engineering. A change that renders perfectly in the developer's Chrome-on-a-fast-laptop can be broken in Safari, unusable on a 360px phone, invisible to a stylus user, or janky on a three-year-old Android. Users don't file bugs — they leave. This skill makes cross-browser, cross-device correctness a *property of how the code is written and tested*, not something a QA pass discovers later (or a user does, in production). The goal is not "test more browsers at the end." It is to write code that is **correct by construction** across environments — standards-based, feature-detected, responsive, and progressively enhanced — and then to *prove* it with automated tests across a real matrix. ## The core principle **Build on the standard, detect the capability, degrade gracefully, and verify on the real matrix.** Every environment gets a working experience; better environments get a better one. You never assume a browser, a screen size, an input device, or a network. If a feature might be missing, you detect it and provide a fallback — you never sniff the user agent and branch on a brand string. ## The workflow ### Step 1: Define the support matrix — decide before you code Read `references/support-matrix-and-targeting.md`. You cannot be "universally compatible" against an undefined target. Establish and commit a matrix: - **Browsers/engines**: the thre