These are the official editing tools by Rebellion for Aliens versus Predator Gold Edition, as well as the source code for the game. It also comes with a complete set of instructions/guidelines for editing. These tools are absolutely essential for editing and creating new content for the game. The source code included in this release is for Gold Edition only. This was officially released by Rebellion in 2001.
If only Rebellion had bothered to update this SDK and provide us a entire whole new SDK with a fully updated new source code for their re-released AvP Classic 2000, then we would have even more and better Mods by now.