function headerValueNormalize (potentialValue) {
  //  To normalize a byte sequence potentialValue, remove
  //  any leading and trailing HTTP whitespace bytes from
  //  potentialValue.
  let i = 0; let j = potentialValue.length

  while (j > i && isHTTPWhiteSpaceCharCode(potentialValue.charCodeAt(j - 1))) --j
  while (j > i && isHTTPWhiteSpaceCharCode(potentialValue.charCodeAt(i))) ++i

  return i === 0 && j === potentialValue.length ? potentialValue : potentialValue.substring(i, j)
}
@see https://fetch.spec.whatwg.org/#concept-header-value-normalize
@param {string} potentialValue
@returns {string}