/usr/share/vim/addons/ftdetect/survex.vim is in survex 1.2.16-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | au BufRead,BufNewFile *.svx setf survex
au BufRead,BufNewFile *.err setf survex-err
|