Pac.vim is a project mainly written in Vim Script, it's free.
syntax highlighting for proxy .pac files
This is a mirror of http://www.vim.org/scripts/script.php?script_id=2249
This is a simple syntax file for highlighting http proxy .pac files. The proxy auto-config file defines how web browsers and other user agents can automatically choose the appropriate proxy server (access method) for fetching a given URL. This script will help to parse these proxy files. A great example to test it out on is at http://www.schooner.com/~loverso/no-ads/. where you can find John LoVerso's outstanding no-ads proxy config file. Let me know what you think, and send comments to my email.