code: function getHeadingTopPos (obj) {
      var position = 0
      if (obj != document.querySelector(options.contentSelector && obj != null)) {
        position = obj.offsetTop
        if (options.hasInnerContainers)
          position += getHeadingTopPos(obj.offsetParent)
      }
      return position
    }
docs: Get top position of heading
  @param {HTMLElement}
  @return {integer} position