Query XML with SQL

I've just learned how to query an xml structure with SQL.
I'm presenting you a simple example. Assuming your XML column looks like this:

<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.xyz.de/activerepository/fileprops">
  <props>
    <prop ns="ARM:" elem="_NoFilter">
      <value xsi:type="xsd:boolean">true</value>
    </prop>
    <prop ns="DAV:" elem="displayname">
      <value xsi:type="xsd:string">Some text in it</value>
    </prop>
    <prop ns="DAV:" elem="getcontenttype">
      <value xsi:type="xsd:string">message/rfc822</value>
    </prop>
    <prop ns="DAV:" elem="creationdate">
      <value xsi:type="xsd:dateTime">2017-01-02T09:38:28.1278078</value>
    </prop>
  </props>
</root>

...you can write this query to get single values from the XML. In my example, I want to query the displayname prop.

SELECT 
  CAST(properties as xml).value('(/root/props/prop[@elem="displayname"]/value)[1]','nvarchar(max)') as [displayname],
  *
FROM   

  tm_cas_files (nolock)

The result will be:

displayname

Some text in it

See also this Stackoverflow link to get more details:
https://stackoverflow.com/questions/48075328/sql-xml-how-to-query-specific-node