Form XML Overview
The XML file contains descriptions of the layout, forms controls, CSS, rules, other elements of the form in a portable format. You can use form XML to migrate from one SharePoint instance to another.
In addition, the form XML import method provides an interface to verify form XML created outside of the Forms designer is valid and can be used by Nintex Forms and Workflow.
When migrating a form from one SharePoint instance to another, you can export the form, transfer the file, and then upload to the target location. It may be helpful in this scenario to understand the content of the form XML, but you will likely only be interacting with the form XML when it has been loaded into the Forms designer designer, or in completing a form in the Forms filler.
You can retrieve the form XML from the Form designer toolbar by using the Import and Export button.You can also access the XML by using the Nintex Forms API and passing the listID and ContentType parameter to an end point to identify the XML you would like to retrieve or update. To understanding this scenario, refer to the Using the NintexFormsPublishExample sample, which explains how to create a WCF client to use the Nintex Forms API.
You can make adjustments to the directly to the XML. For example, you may want to update the Form CSS, a logo, or other element stored in the form description. Provided the form XML remains valid you can then load the modified XML back into Nintex Forms with your updates.