It turns out that the error I got trying to access the XSLT source (not the missing shortcut, the crash) was due to a bug in the editor. I had a
with no <tbody>. Yes, I know.
But the editor checked the XSLT and appears to think it is fine. Then the renderer took over and crashed, due to the missing <tbody>.
Fortunately I found the XSLT in the temp cache so with the supplier’s help I could regenerate the XSLT (deleting all my work) and reinsert my code, now with the <tbody> tag.