I have a number of .xml files in my project which I can view and open in ST3 when selecting from explorer but they are not showing in the sidebar.
What do I need to do to make files, irrespective of extension, show in the sidebar?
The file_exclude_patterns setting controls what files are hidden in the sidebar. Open your main Settings file and see if xml was added to the list.
It is also possible that some package you have installed includes a preferences file that hides XML files. You could test this by moving your data folder to a backup location, as described at http://www.sublimetext.com/docs/3/revert.html. Just be sure to move it and not delete it, so you may restore it after testing.
Excellent. That worked. Thank you.