cdpath

How does the 'cd Sites' command below work?
cd /System
ls
Library
cd Sites
ls
Tips Tutorials archive areas css frames images index.html
pwd
/Users/saruman/Sites

The command 'cd Sites' should not work, but it has managed to change directory to 'Sites' in my home directory. This behaviour is controlled by the shell variable 'cdpath'
set cdpath= ( ~ ; ~/Sites )

Tells 'cd' that if it can't find the requested directory in the current directory, search my home directory (~), and then ~/Sites