Navigator 2.0; implemented but nonfunctional in Internet Explorer 3.0
document.referrer
referrer is a read-only string property that contains the URL of the document from which the current document was reached. For example, if the user follows a link in document A to document B, then in document B, the Document.referrer property contains the URL of document A. On the other hand, if the user types the URL of document B directly and does not follow any link to get there, then the Document.referrer property for document B will be an empty string.