Though there are several groups catergorized into Miao such as the Hmu, A Hmao,and Kho (Qho) Xiong, can anyone here explain their differences? Are there any pictures differentiating their clothing and head-dress? Language-wise, what varies and what is similar?

I am particularly interested in the Hmu since I cannot find much information in Western documents. Any help would be greatly appreciated. Please stay on-topic and don't turn this into another Miao/Hmong thread about politics, nationalism, and revisionist history.