use of an undeclared "impl" namespace?

[Madeleine Wright <m....@ru.ac.za>]

I'm fairly new to Axis.  I wrote a simple Java service class with a main
method.  The wsdl file that was generated with the "?wsdl" appended to the
url contained this:
<wsdl:message name="mainRequest">
    <wsdl:part name="args" type="impl:ArrayOf_xsd_string"/> 
</wsdl:message>

I can see that "args" are the parameters: but why is the namespace "impl"?
It isn't declared earlier.  Please can someone explain what the "impl"
namespace is?  (I have searched on the Internet but can't find anything
specific.)

Thanks.

Madeleine