code: function elementTrailingWhitespace(el) {
    let style = getComputedStyle(el, null)
    let display = style.getPropertyValue('display')
  
    let lastNotIgnoredChild = () => {
      for(let i = el.children.length - 1; i >= 0; i--) {
        let n = el.children[i]
        if(!ignoredNode(n)) return n
      }
      return null
    }
  
    if(display === 'inline') {
      let last = lastNotIgnoredChild()
      if(last && last.nodeType === Node.ELEMENT_NODE) {
        let lastChunks = []
        innerRichText(last, lastChunks)
        return elementTrailingWhitespace(last, lastChunks)
      } else {
        return ''
      }
    } else if(display === 'inline-block'
      || display === 'inline-table'
      || display === 'none'
      || display === 'table-column'
      || display === 'table-column-group') {
      return ''
    } else if(display === 'table-cell') {
      return '\t'
    } else {
      let elChunks = []
      innerRichText(el, elChunks)
      if(elChunks && elChunks.length > 0) {
        let marginBottom = getPixelStyleProperty(style, 'margin-bottom')
        let fontSize = getPixelStyleProperty(style, 'font-size')
        if(marginBottom >= fontSize / 2) return '\n\n'
        else return '\n'
      } else return ''
    }
  }
docs: https://rawgit.com/timdown/rangy/master/fiddlings/spec/innerText.htm#trailing-whitespace
  @param el