code: func ByClass(class string) Matcher {
  	return func(node *html.Node) bool {
  		classes := strings.Fields(Attr(node, "class"))
  		for _, c := range classes {
  			if c == class {
  				return true
  			}
  		}
  		return false
  	}
  }
docs: // ByClass returns a Matcher which matches all nodes with the provided class.