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

What if depObj is neither a FrameworkElement or a FrameworkContentElement? I don't know the full scenario (i.e. what the types are likely to be), but this seems a reasonable defensive strategy.