Tiebreaker 6: The platform before the framework
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Spec: descriptive guidance, not a checkable rule.
It carries no forbidden and instead pair, and no `jig check` detector applies to it directly.
Section: Principles
Group: Tiebreakers

**When the browser can already do it, use the browser.**

`<dialog>`, `<details>`, `position: sticky`, `:has()`, container queries, native form validation, `popover`. Platform features carry accessibility, keyboard handling and state management that a reimplementation gets wrong and then needs maintaining.