The DV User Manual indicates that the output file argument to each of the layout options can be omitted, in which case DV will create an output filename based on the layout filename.
However, in reality DV requires an output filename following a layout switch on the command line.
This request is to either change the documentation to match the code, or vice versa. CUrrently
datavision -h -n somereport.xml
fails, whereas the manual suggests it should work.
The workaround for now is to do
datavision -h somereport.html -n somereport.xml