Q: What is DRL?
drl is the "drools rule language" which the past was natively XML, and now is not.
Q: Why not XML?
The XML in the past had XMLSchema to help validate the content, but essentually it didn't add value to what was defined in the actually pointy end of the rule. Also, XML gives me headaches. There aren't common graphical XML editors available in the open source world (things similar to Oxygen and XML Spy) so most people end up editing XML by hand, which is un pleasant.
Q: Will you support XML?
Yes there is an XML language as well now. RuleML support is planned shortly.
With the XML support, you can import and export to from the various formats.