How are Scala <: <and =: = used and how does their implementation in Predef work?

Question

Possible duplicate:
What to do <: <, <% <, and =: = average in Scala 2.8 and where are they documented?

Obviously, <: <and =: = are used to state that two types are subclass related or equal. But the documentation is not clear how they are used, and a Google search is almost impossible, given that they consist solely of characters. (However, another reason why such names with the -goo symbol is a bad idea.)

Also, how does their implementation in Predef work? I was very surprised to learn that they are not built-in, because I did not understand that Scala allows you to create statements that act on types in this way - which function in Scala allows you to do this? And the implementation in Predef is completely opaque. Is there some kind of compiler magic here?