In Dynamics 365 Portal you can write FetchXML query in Liquid using the fetchxml tag. As this query can be dynamically constructed, there may be scenarios where you will need to debug it. There’s an undocumented feature that allows you to view the actual XML that Portal executes against CRM.
Here’s an example. Let say I have a page that takes a query string and uses Fetch to list all accounts where account name starts with that string. I would like to view the actual FetchXML being executed in order to debug the page. I can do this by simply accessing the xml property of the query object. Below is the Liquid code for this.

Here is how the page renders:

As you can see, this can be a very useful tool for debugging. Note that in the Liquid code, the escape filter is used to escape the XML tags. Without this, the XML will still be output, but will not be displayed on the page when viewing in browser.

This works for both OnPrem and On Cloud Portals.