When you are modding XML files, the game should check for all kinds of missing definitions when it loads your XML. It checks for some, but not all. If you have used a symbol but the definition is missing, the game may randomly crash, either at startup or during play. This checker tries to catch all kinds of missing definitions so your mod doesn't crash. See the user documentation for full details. I have submitted it to the forum download page, but it is in the "moderation queue". You can download the latest version of the program from this link.