htmlunit-core-js.jar is a modified version of Mozilla Rhino (http://www.mozilla.org/rhino/) which was initially developed by Netscape Communications Corporation. The changes to the source code are provided in the file rhinoDiff.txt (and can be generated by calling cvs diff in the rhino folder). This software is provided by the HtmlUnit team "as is" under the MPL 1.1 license, available at http://www.mozilla.org/MPL