Data Value Type: Codeunit
With the Type: Codeunit a value from a table can be defined individually. Programmed functions, filters and other things can be used for this.
Example
When the customer uses a code unit for merging lines or a codeunit for other logics for a posted sales invoice, then you also need a codeunit for XSD. Otherwise, there is a very high chance that an invalid XML file will be created for XInvoice and ZUGFeRD formats.