Missing php-xml

[hactar]

We're trying to activate a vtiger module, however its not working, and according to the documentation it requires:

vtigerCRM version ( 7.1.0)
• Zip Archive Package Library installed at server.
• DOMDocument (php-xml) Package Library installed at server.

If I read the php_info correctly, zip support is in, however there is no php-xml module? Can we include it somehow or does this need to be adjusted in the image itself?