vim blockdiag filetype detection

gistfile1.txt

" blockdiag
autocmd BufRead,BufNewFile *.diag
   \ let s:line1 = getline(1) |
   \ if s:line1 =~ '\<diagram\|blockdiag\>\s*{' |
   \     set filetype=blockdiag |
   \ elseif s:line1 =~ '\<seqdiag\>\s*{' |
   \     set filetype=seqdiag |
   \ elseif s:line1 =~ '\<actdiag\>\s*{' |
   \     set filetype=actdiag |
   \ elseif s:line1 =~ '\<nwdiag\>\s*{' |
   \     set filetype=nwdiag |
   \ elseif s:line1 =~ '\<rackdiag\>\s*{' | |
   \     set filetype=rackdiag |
   \ elseif s:line1 =~ '\<packetdiag\>\s*{' |
   \     set filetype=packetdiag |
   \ endif |
   \ unlet s:line1