CONTENT_LENGTH Number of characters submitted from a POST command
HTTP_REFERER URL user came from, if available.
HTTP_USER_AGENT Type of Browser viewer is using, if available.
QUERY_STRING String in URL after the ? character
REMOTE_ADDR Remote user's IP address
REMOTE_HOST Name of user's host, if available.
SERVER_NAME Name of the local server, like: www.yoursite.com
