Is there more to the C# “as” keyword than simple casting?

Question

I\'m working through Josh Smith\'s CommandSink code obviously do not understand something about the \"as\" keyword in C#.

I don\'t understand why he wrote the line:

Answer 1

IsValid = _fe != null || _fce != null;

and

IsValid = depObj != null;

are not the same tests because if depObj is not of type FrameworkElement nor FrameworkContentElement but is not null the second test will return true, while the first will return false.