code: function getTextNodes(el) {
    el = el || document.body
  
    var doc = el.ownerDocument || document
      , walker = doc.createTreeWalker(el, NodeFilter.SHOW_TEXT, null, false)
      , textNodes = []
      , node
  
    while (node = walker.nextNode()) {
      textNodes.push(node)
    }
    return textNodes
  }
docs: return all text nodes that are contained within `el`