JSFiddle - React, Tailwind, and code Playground
JavaScript
var re = `<span>(?:[^<]|<(?!span>|\/span>)|(?R))*<\/span>`;
var s = re;
for (let i = 0; i < 10; i++) {
s = s.replace('(?R)', re);
}
s = s.replace('|(?R)', '');
console.log(new RegExp(s, 'g'))