WotLK Battleground matching

[NKTPlayz]

Hi, I saw that on warmane you have brackets for battlegrounds. Right now I'm on the lower bracket cause I'm fresh 80, but I seem to find players with low gear but with donated Wrathfull weapons. So whats the catch ? I can use no BiS items, but 277ilevel is ok ? Can someone explain how the brackets work with low iLevels :)

[Thorbjorn]

It's not public knowledge to avoid twinking in those brackets.