<extension> functions   

Hi
Can someone tell me how is it about e.g. 
System.Collections.ObjectModel.Collection
function ToArray: I need to know if such "extension" function is standart to 
all .NETs, or if it is reasonable to use this in DLL targeted to help most of 
.NET programmers.
Thx

date: Fri, 8 Aug 2008 10:39:01 -0700   author:   konikula