<tag att1="one" att2="two">
  content
</tag>

<tag att2="two" att1="one">
  content
</tag>

$ xmllint --c14n one.xml > 1.xml
$ xmllint --c14n two.xml > 2.xml
$ diff 1.xml 2.xml

xmllint --format one.xml > 1.xml
xmllint --format two.xml > 2.xml
diff 1.xml 2.xml

$ xmllint --exc-c14n one.xml > 1.xml
$ xmllint --exc-c14n two.xml > 2.xml
$ diff 1.xml 2.xml

$ xmllint | grep c14
    --c14n : save in W3C canonical format v1.0 (with comments)
    --c14n11 : save in W3C canonical format v1.1 (with comments)
    --exc-c14n : save in W3C exclusive canonical format (with comments)

$ rpm -qf /usr/bin/xmllint
libxml2-2.7.6-14.el6.x86_64
libxml2-2.7.6-14.el6.i686

$ cat /etc/system-release
CentOS release 6.5 (Final)