Template Parts is a lightweight “ponyfill” that brings the upcoming Template‑Instance proposal to current browsers. It lets developers define placeholders like `{{x}}` inside `<template>` markup, instantiate them as a `DocumentFragment` via `new TemplateInstance(...)`, and later update the values (including boolean attributes) through a simple processor API. This library is aimed at web developers building component‑style UI who want reactive template interpolation today while remaining compatible with the future spec.