title: What do <:<, <%<, and =:= mean in Scala 2.8, and where are they documented?
body: <p>I can see in the API docs for <a href="https://scala-lang.org/files/archive/api/2.8.2/scala/Predef$.html" rel="noreferrer">Predef</a> that they're subclasses of a generic function type (From) => To, but that's all it says.  Um, what?  Maybe there's documentation somewhere, but search engines don't handle "names" like "&lt;:&lt;" very well, so I haven't been able to find it.</p>
  
  <p>Follow-up question: when should I use these funky symbols/classes, and why?</p>