Although it would be awesome if the extension could load in and swap XML's at runtime, it would also be fine for most games if it could only do so within the construct frame editor.
So, the absolute necessities are:
1) it could load in the XML file that you assign it to.
2) It would either pre-load all the images from all the folders into its own data "bank" or be able to do so at load time of a frame. (both would be great, but if necessary the first option only)
3) You could assign a "character" from my tool's XML to a standart construct sprite. It would become a "child" of the construct sprite.. and copy its rotation, position, general opacity etc... In theory, the standard construct sprite would not only be used to control the "characters" basic stuff AND could be used as a basic full body collision (such as a rectangle for a platformer engine)
3) It would allow for changing and keeping track of the animation that is playing in the character.
4) It would keep track of that Characters variable and per frame variable changes
5) It would handle detection of colisions between colision rectangles between that character and any other character assigned to any other construct sprites.
6) it would also keep track of the XML's action points for such uses as spawing bulettes and anchoring other sprites at that actionpoints location.