Enabling PHP Syntax Highlighting for .html Files in vim

vim has a lot of default file types and syntax dictionaries set up. It determines which syntax highlighting to do based on a files extension. I have a bunch of .html files that contain PHP code and finally got frustrated enough with the incorrect highlighting to figure out how to correct it. After bit of research and experimentation, but I was finally able to do it by creating ~/.vim/filetype.vim with this content:

    if exists("did_load_filetypes")
      finish
    endif
    augroup filetypedetect
      au! BufRead,BufNewFile *.html     setfiletype php
    augroup END