Accessing the DOM from UPX plugins

I am trying to convert some Extendscript functions into the UPX environment but I'm having trouble accessing the DOM.  For instance this code worked with Extendscript

var orig_ruler_units = app.preferences.rulerUnits;
var orig_type_units = app.preferences.typeUnits;

app.preferences.rulerUnits = Units.PIXELS; 
app.preferences.typeUnits = TypeUnits.POINTS; 

But these same lines of code error out in the plugin because the attributes don't exist.  Is there any documentation on what is accessible via the UPX environment?  I know how I can find these for use via batchplay but if I can go through the DOM I would prefer that approach.