func (s *Selection) Attr(attrName string) (val string, exists bool) {
	if len(s.Nodes) == 0 {
		return
	}
	return getAttributeValue(attrName, s.Nodes[0])
}
Attr gets the specified attribute's value for the first element in the
Selection. To get the value for each element individually, use a looping
construct such as Each or Map method.
package goquery
import (
	"bytes"
	"regexp"
	"strings"
	"golang.org/x/net/html"
)
var rxClassTrim = regexp.MustCompile("[\t\r\n]")