This is a modified version of StanceSets Extended which was originally written by capnbry, and modified by Smuggles.

This add-on allow you to quickly swap weapons and shield on a single key press,
and cycles between two or three different weapons sets.
Additionaly this add-on can have different weapons sets cycle for different stances and shapes.

Reference:
http://capnbry.net/wow/
http://www.curse-gaming.com/mod.php?addid=151
http://www.curse-gaming.com/mod.php?addid=1136

---------Original description by capnbry----------
Typing /stancesets will open the stance set configuration dialog. Drag and drop the weapons you want equipped for each set into the containers, starting from the left. If you want to make sure the first set is in your hands when you assume that stance / form, check the "Equip first on activate". If you do not have this checked, and the weapons in your hand match one of the sets from your new stance, no swap will occur. To remove a weapon, drag it off the slot.

Up to 3 sets of weapons can be available for each stance. To cycle through them, use "/stancesets next". The addon will loop around to the beginning of the list when it sees the first empty mainhand slot, so:
weapon1,weapon2 blank,weapon3 weapon4, weapon5
will not cycle at all if your hands are already holding weapon1 and weapon2. If you don't have any matching set in your hand when you call "next", the first set will be put in your hands.

The panel toggle and set cycle can be bound to a key combination.
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StanceSets v3