How to use the react-overlays/lib/Position.propTypes function in react-overlays

import React, { Component, PropTypes } from 'react'
import RootCloseWrapper from './RootCloseWrapper'
import Portal from 'react-overlays/lib/Portal'
import Position from 'react-overlays/lib/Position'
import Transition from '../components/Transition'
import ScreenReaderContent from '../components/ScreenReaderContent'

export default class Overlay extends Component {

  static propTypes = {
    ...Portal.propTypes,
    ...Position.propTypes,

    /**
     * Set the visibility of the Overlay
     */
    show: PropTypes.bool,
    /**
     * Specify whether the overlay should trigger `onHide` when the user clicks outside the Overlay
     */
    rootClose: PropTypes.bool,

    /**
     * Specify whether the overlay should render offscreen (visible to screen readers) when not shown
     */
    renderOffscreen: PropTypes.bool,

    /**