title: What are the differences between extern, abstract, and partial for methods in an abstract class?
body: <p>I am writing an abstract class because I want to provide a few commonly used methods, require a few methods that will be too specific, and allow some methods to "extended".  After bumping into a compiler error I am wondering if anybody can explain the differences between the <em>extern</em>, <em>abstract</em>, and <em>partial</em> keywords.  What do they mean and when/where should I use them?</p>