code: function getTextContent(node) {
    if (isCommentNode(node)) {
      return node.data || '';
    }
    if (isTextNode(node)) {
      return node.value || '';
    }
    var subtree = nodeWalkAll(node, isTextNode);
    return subtree.map(getTextContent).join('');
  }
docs: Return the text value of a node or element
  
  Equivalent to `node.textContent` in the browser