comman!-narg=* Xexpr <mods>lex<args>
auto BufReadPre * exe"sn" ..expand("<abuf>") 
fu Xautocmd_changelist()
cal writefile(['Xtestfile2:4:4'],'Xerr')
  sil! edi Xerr
Xexpr 'Xtestfile:4:4'
endf
call Xautocmd_changelist()
call Xautocmd_changelist()