Versions of WebCopy up to 1.0.1.4 read and wrote project data as XML, support for reading these files was removed since version 1.1.2.203. Documentation for this format is not available.
WebCopy 1.0.2.0 and above use named binary tags (NBT) for storing project data and can be inspected or modified using standard NBT editing software. Documentation for this format is pending.