+ * *pad=*_filename_ when this is given as first argument, the fused
+ file is set up as a writable random-access file, where the write
+ events are captured appended to the nominated "pad" file. The new
+ content is inserted into the fused file but not the original files,
+ and fragments are split up and adjusted as needed so as to make the
+ write events appear as insertions inteo the fused file.
+