[DFDL-WG] Policy Driven DFDL?

Suppose you have an XSLT stylesheet with a bunch of global variables. Suppose that the value of those variables must be determined outside of the XSLT. How do you get the values into it? You might use parameters, and pass in the values when you call the transform() function in your code. But you could also use the document() function from within XSLT, read in an XML "policy" file that has all the values, then store the values in the variables. You might call this approach policy driven XSLT. Can we do policy driven DFDL? Yes, I know that we have parameters, but is there a way to read in a "policy" file (whether XML or not), read the values, then set the variables to those values? TIA