tailwindcss/src/plugins/tracking.js

import _ from 'lodash'

export default function () {
  return function ({ addUtilities, config }) {
    const utilities = _.fromPairs(_.map(config('tracking'), (value, modifier) => {
      return [`.tracking-${modifier}`, {
        'letter-spacing': value,
      }]
    }))

    addUtilities(utilities, config('modules.tracking'))
  }
}