message: export propTypes from utility mapping functions
  This adds a propTypes object to functions for mapping responsive
  utilities. It presumes that any value can be either a single number or
  array of numbers, and exports some helpers for declaring similar prop
  types.
diff: +import PropTypes from 'prop-types'
  import classnames from 'classnames'
  import createMapper from 'system-classnames'
  @@ -5,7 +6,23 @@ const breakpoints = [null, 'sm', 'md', 'lg', 'xl']
  const call = (f, v) => (typeof f === 'function') ? f(v) : f || v
  -const map = createMapper({
  +export const oneOrMoreOf = type => PropTypes.oneOfType([
  + type,
  + PropTypes.arrayOf(type)
  +])
  +
  +export const oneOrMoreNumbers = oneOrMoreOf(PropTypes.number)
  +
  +export const createMapperWithPropTypes = config => {
  + const mapper = createMapper(config)
  + mapper.propTypes = config.props.reduce((propTypes, prop) => {
  + propTypes[prop] = oneOrMoreNumbers
  + return propTypes
  + }, {})
  + return mapper
  +}
  +
  +const map = createMapperWithPropTypes({
  breakpoints,
  props: [
  'm', 'mt', 'mr', 'mb', 'ml', 'mx', 'my',
  