there are many different XML supported and used by j661, i.e. these are files which all have different DTDs or schemas.
Every once in a while I actually managed to pick the wrong type of XML file for the task at hand, and j661 cannot currently handle this too well.
I guess it would make sense to look for some tags/attributes in the XML file and automatically recognize that the chosen file has the wrong format.
And then there should ideally be an error message saying "This is not the right type of XML file". Currently, it is possible to halt the editor by picking the wrong type of XML file,