One issue I ran into early on was wanting more than one filetype’s snippets available for a single file. In my case, I was editing a file with a .php extension, but it had a lot of HTML in it as well. Since the filetype is determined from the extension, I only had the snippets for PHP. To fix this, I added a file ~/.vim/ftdetect/php.vim, containing:\\r\\n\\r\\nWhen a file with an extension matching a filename in ftdetect is opened, its filetype can be changed to whatever is desired via a directive like the one above. The dot separating the filetypes allows for multiple formats to be made available at once.

au BufRead,BufNewFile *.php set filetype=php.html