The "Button Name" field is the label that will appear on the Menu in the XML Editor. This will not change or affect the actual XML file at all, only the name of the button. baseURL allows you to set a "root" path for the files contained in this XML file. Sometimes, people set up the XML file to only hold a partial path, such as the file name only, when the full path to the image might be longer.

For example, the XML file might only hold the data image.jpg, while the full path is actually media/newimgs/image.jpg. In this case, I could set the baseURL as media/newimgs/, and the XML editor will act as if the full path existed, and will allow the file to load and be edited.