React: What is React useInsertionEffect?

1import { useInsertionEffect, useRef } from "react";
2
3function useCSSAnimation(name, keyframes) {
4  const styleRef = useRef();
5  useInsertionEffect(() => {
6    const style = document.createElement("style");
7    style.textContent = `@keyframes ${name} { ${keyframes} }`;
8    document.head.appendChild(style);
9    styleRef.current = style;
10    return () => { styleRef.current.remove(); };
11  }, [name, keyframes]);
12}