Domains in asp.net

Hello friends,

 

Im learning for the mcp test,And one of the section include domains & Assemblies,

My question are:

1 Is there  use for domains in asp? maybe to run 3 party services?

2 The following code work fine.. How could it be that an interface type(IPermission )

  is acting like normal class? Firstly i thought that if there is an interface return type then the return object

  should implemented by this interface but it seem im wrong...

 
Zone z1 = new Zone(System.Security.SecurityZone.Internet);
System.Security. ...