ES2 Mudlib uses vim's modeline to support LPC syntax hightlight.
You can download the syntax highlight settings for vim from LPC Syntax Highlight. This download page also gives you instructions about how to install the settings.
Remember to enable modeline for vim in your .vimrc:
set modeline
In ES2's LPC programs, you may see the first line containing:
// vim: syntax=lpc
This line tells vim to syntax highlight the file with LPC syntax instead of regular C language.