Browser support

Required, no fallback: the Popover API, inert, and clip-path: path(). That puts the floor at roughly Chrome 117, Safari 17.5 and Firefox 129.

CSS anchor positioning is the one piece that isn’t everywhere yet (Chrome 125+, Safari 26+, Firefox 147+), and the one piece with a fallback. strategy: 'auto' uses the native tether where it exists and a measured positioner everywhere else. It also verifies the anchor actually resolved, and falls back mid-step if it didn’t.

import { supportsAnchorPositioning } from '@cmunns/guidepost';

supportsAnchorPositioning(); // true on the native path

the live demo tells you which path your browser is on.