As Veev - original author of TabBinder - will not update it anymore. I taken over (with his consent) his project. I fixed code for 4.x, added support for new BG and made entire add-on locale independent.

RETabBinder will automatically change your tab key binding to only target enemy players when in PvP zones, and to target all enemies when not.

Despite it being named RETabBinder it will also work for keys other than just tab. First it will check to see if you currently have target nearest enemy player bound, if not then it will check for target nearest enemy (the default tab behavior). If you have either of those already set then it will use your current key binding to alternate between the two different functionalities, if not then it will resort to tab.

No configuration needed so there is no options menu, just install it and you're good to go. It will switch to players only when in arenas, battlegrounds, Wintergrasp and Tol'Barad, and when entering a duel. Great for those of us that like to both PvE and PvP... no more tabbing through totems after forgetting to set it, or wondering why you can't change targets in a raid.

Available commands:
/rtb default - Turn off/on default bindings.
When this option is turned off RETabBinder will not overwrite empty keybinds with TAB/Shift-TAB.