code: func FindPrevSibling(node *html.Node, matcher Matcher) (n *html.Node, ok bool) {
  	for s := node.PrevSibling; s != nil; s = s.PrevSibling {
  		if matcher(s) {
  			return s, true
  		}
  	}
  	return nil, false
  }
docs: // Find returns the first node which matches the matcher using previous sibling search.
  // If no node is found, ok will be false.
  //
  //     root, err := html.Parse(resp.Body)
  //     if err != nil {
  //         // handle error
  //     }
  //     matcher := func(n *html.Node) bool {
  //         return n.DataAtom == atom.Body
  //     }
  //     body, ok := scrape.FindPrevSibling(root, matcher)