Q: Why did Phoenix move to the multi attachment system?
A: In the past, Phoenix used an unofficial modification to one of the viewer's XML files to provide additional attachment points. This modification worked fine for all viewers that used the same altered XML file, but residents with other viewers, such as Linden Lab's original viewer, saw these additional attachment points randomly floating around the avatar, or not at all. The new Viewer 2 multi attachment system is the official Linden Lab way of attaching multiple items to a single attachment point. To stay compatible with future releases of the Second Life system, Phoenix has adopted this new functionality.
Q: How is the multi attach system different from the old way Phoenix used?
A: Phoenix does no longer provide duplicated attachment points (like pelvis 2). Instead, you will see a new context menu item in your inventory that allows you to add attachments to a point, rather than just wear and replace it. So, if you want to wear a belt and a tail on the Pelvis, you can attach the belt, then right click on the tail and select “Add”.
Q: How many attachments can I wear on one spot?
A: You can wear a maximum of 38 attachment points overall. Within this, you can put as many as you like on any attachment point at the same time.
Q: Does this feature also let me wear multiple clothing layers?
A: No, multiple clothing layers won't be implemented until the release of Firestorm.
Q: How will this new system affect me?
A: That depends on your avatar. If you didn't use any multiple attachments before, you won't see any difference at first. If you used the deprecated Phoenix attachment points, those attachments will be detached, and you will have to reattach them the first time you log in with a multi attachment enabled Phoenix version.
Q: Will this have an effect on RLV?
A: Most of the current RLV implementation will behave the same as before. To work with the new system, the RLV specification has been extended and does now contain additional commands to use with multi attachments.
Q: Will everyone see my attachments correctly?
A: Everyone using a viewer that implements the V2 multi attachment standard will see your attachments correctly. Viewers that don't offer this functionality yet will only display one of the items you attached to the respective spot. For backwards compatibility, Phoenix will continue to display attachments on the deprecated Phoenix attachment slots correctly, until the new, official method has become widely used.
Q: Do other Third Party Viewers have this system?
A: Yes. A number of other third party viewers already implemented this functionality, e.g. Imprudence, Kirsten's and Cool Viewer.
Q: Who wrote the code for the Multi attachment system?
A: The base implementation was done by Henri Beauchamp, Phoenix implementation by Kitty Barnett.
See here for information on migration to this system.