An UDF_Gen description file specifies anything down to the actual function code (including parameter passing) in a rather simple XML format.

While implementing an UDF one no longer needs to implement all the boring repetitive interface stuff but can start with the actual functionality right away.

The <udf> tag is the top level tag of every extension description. The name of the extension is specified in its name attribute. A minimal extension looks like this:

<?xml version="1.0"?>
<udf name="x1"/>