Returns previous sibling node that is not a blank text node
function _getPreviousSiblingThatIsNotBlank(node) {
    var previousSibling = node.previousSibling;
    while (previousSibling && _isBlankTextNode(previousSibling)) {
      previousSibling = previousSibling.previousSibling;
    }
    return previousSibling;
  }