What is this UNIXMODE stuff anyway?

[Xav <MBGE4MDC@fs1.ee.man.ac.uk>]

Sorry guys, another newbie question. Over the past few months, I've 
read a lot about the UNIXMODE variable. What is it, where is it, and 
what does it do? From the recent ELM discussions, it sounds like it 
_might_ help out with some of my problems, but is it just an 
environment variable, or is it something in a header file somewhere 
for use at compile time? Where can I find out more about what it 
does?

Cheers,

Xav <mbge4mdc@fs1.ee.man.ac.uk>