Why should include encodingStyle wirh attachment?

[Jue \(Jacky\) Shu]

hi all

as far as i know, namespace http://schemas..xmlsoap.org/soap/encoding/ defines array 
datatype,
so when we use arry in axis, we should include 
"encodingStyle="http://schemas..xmlsoap.org/soap/encoding/"; in wsdd.
but when we deals with attachments, why should we also includes this namespace in 
wsdd?
thx a lot.

Jacky