function isValidClientWindowBits (value) {
  for (let i = 0; i < value.length; i++) {
    const byte = value.charCodeAt(i)

    if (byte < 0x30 || byte > 0x39) {
      return false
    }
  }

  return true
}
@see https://www.rfc-editor.org/rfc/rfc7692#section-7.1.2.2
@description "client-max-window-bits = 1*DIGIT"
@param {string} value
@returns {boolean}