how Go handles multiple x509/ssl certificate common names

cert.txt

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            61:02:d2:d6:00:00:00:00:00:15
    Signature Algorithm: sha1WithRSAEncryption
        Issuer: C=US, ST=Washington, L=Redmond, O=Microsoft Corporation, CN=Microsoft Product Secure Server CA/[email protected]
        Validity
            Not Before: Aug 13 21:20:05 2010 GMT
            Not After : Nov 13 21:20:05 2011 GMT
        Subject: C=US, ST=WA, L=Redmond, O=Microsoft, OU=MIH, CN=*.validation.sls.microsoft.com, CN=validation.sls.microsoft.com, CN=*.activation.sls.microsoft.com, CN=activation.sls.microsoft.com, CN=sls.microsoft.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:ac:ec:40:32:db:c7:d7:3c:99:87:7c:2d:9b:3b:
                    53:5a:8c:e4:42:58:e6:a3:b5:87:88:c7:40:4f:57:
                    a6:4e:92:44:01:a3:6d:3c:b7:6e:42:7e:a5:b0:8b:
                    39:90:82:99:08:e4:28:b9:f1:e9:a4:5a:44:b2:48:
                    98:23:fa:63:14:ab:44:84:72:28:75:6a:47:a2:81:
                    a5:4f:ad:66:86:68:5e:43:68:d9:62:40:bd:c6:68:
                    62:ce:ce:09:7b:42:5c:aa:0c:b0:71:82:4f:dc:e4:
                    b3:61:e5:73:1a:b1:18:d8:f9:47:52:d2:c8:a2:a4:
                    68:ac:3a:e9:c5:cf:6f:eb:f3
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Key Usage: critical
                Digital Signature, Non Repudiation, Key Encipherment, Data Encipherment
            X509v3 Extended Key Usage:
                TLS Web Server Authentication
            X509v3 Subject Key Identifier:
                F8:A3:22:F3:E5:C2:AF:5B:39:08:63:02:A5:D6:5C:3C:CF:BF:F3:BD
            X509v3 Authority Key Identifier:
                keyid:9E:49:93:71:E6:FA:ED:97:80:08:89:3E:3C:F3:29:CC:71:6D:EF:5C

            X509v3 CRL Distribution Points:

                Full Name:
                  URI:http://crl.microsoft.com/pki/crl/products/MicProSecSerCA_2007-12-04.crl
                  URI:http://www.microsoft.com/pki/crl/products/MicProSecSerCA_2007-12-04.crl

            Authority Information Access:
                CA Issuers - URI:http://www.microsoft.com/pki/certs/MicProSecSerCA_2007-12-04.crt

    Signature Algorithm: sha1WithRSAEncryption
         1a:20:cf:e4:49:04:90:45:da:ac:7d:80:df:68:c7:28:52:d8:
         3e:3d:e5:c8:30:6f:fd:bf:e5:fa:48:12:42:77:a8:3b:07:16:
         de:ec:95:f3:bc:2a:f3:4a:e7:f1:16:7a:30:ca:cc:05:23:9f:
         33:1d:37:b9:69:9c:5f:ec:cf:86:01:84:1e:04:9f:c7:90:bc:
         c5:21:39:5f:18:4d:77:01:ae:4e:e2:5f:a2:e9:8d:d6:88:d4:
         72:6b:d8:d6:22:26:41:a6:58:40:b6:7a:23:68:50:29:2e:e4:
         3a:5c:d2:af:72:01:14:33:5f:16:89:9c:e3:30:1a:f3:13:b0:
         72:0e:3c:f5:6c:0d:5f:de:eb:65:13:3e:62:2f:77:fa:50:51:
         d0:38:7e:a9:69:cb:6f:08:1f:95:ec:c4:a0:aa:b6:c2:17:b7:
         c9:ae:2d:f9:bc:f3:b0:92:53:42:c0:cd:6d:ff:65:67:40:de:
         de:f5:9e:d3:b6:f6:2a:de:c8:2d:f0:33:f1:e9:b9:e7:d3:2d:
         a5:9a:4a:35:c7:5a:52:ad:dc:af:b4:fc:c5:bd:75:61:fc:b8:
         50:20:f6:07:9e:03:22:bb:6e:a1:4c:02:66:f5:b9:cf:30:01:
         28:b0:c7:c6:78:ea:f0:09:1b:1b:54:0a:28:71:3e:4f:f6:99:
         2a:20:2e:58

cn.go

package main

import (
	"crypto/x509"
	"encoding/asn1"
	"encoding/pem"
	"fmt"
	"io/ioutil"
)

var cnType = asn1.ObjectIdentifier{2, 5, 4, 3}

func main() {
	pemBytes, _ := ioutil.ReadFile("ms.pem")
	pem, _ := pem.Decode(pemBytes)

	cert, err := x509.ParseCertificate(pem.Bytes)
	if err != nil {
		fmt.Println("could not parse cert: %s", err)
		return
	}

	fmt.Println("Common Name:", cert.Subject.CommonName)

	for _, name := range cert.Subject.Names {
		if name.Type.Equal(cnType) {
			fmt.Println("  Extra Common Name:", name.Value)
		}
	}
}

ms.pem

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----