C# VS2012 references, adding a Class Library?

C# VS2012 references, adding a Class Library?

Why is it that if you have a Class Library in your solution, the only way
to reference it so that the VS2012 will recognize the classes within it,
is by going into references and choosing the class from the projects tab.
Why can you not instead compile the Class Library separately and use the
generated .dll and add that through the browse tab, note: that I am still
assuming that the Class Library still exists as a separate project in your
solution.