1. Not sure it matters since all formats get converted to the video cards internal format, try png, as it is not lossy and supports alpha layers.
2. Search for forum posts when the feature was introduced, it will have info on what the xml needs to have to trigger this.
3. Not yet.
4. Not yet.
5. Search for forum posts when the feature was introduced, it will have info on what the xml needs to have to trigger this.