Words about Predef in REPL

_overviews/repl/overview.md

@@ -27,23 +27,47 @@ The REPL also provides some command facilities, described below.
 An alternative REPL is available in [the Ammonite project](https://github.com/lihaoyi/Ammonite),
 which also provides a richer shell environment.
 
+### Features
+
 Useful REPL features include:
 
   - the REPL's IMain is bound to `$intp`.
   - the REPL's last exception is bound to `lastException`.
   - use tab for completion.
   - use `//print<tab>` to show typed desugarings.
   - use `:help` for a list of commands.
+  - use `:load` to load a file of REPL input.
   - use `:paste` to enter a class and object as companions.
   - use `:paste -raw` to disable code wrapping, to define a package.
   - use `:javap` to inspect class artifacts.
   - use `-Yrepl-outdir` to inspect class artifacts with external tools.
   - use `:power` to enter power mode and import compiler components.
+  - use `:settings` to modify compiler settings; some settings require `:replay`.
+  - use `:replay` to replay the session with modified settings.
 
 Implementation notes:
 
   - user code can be wrapped in either an object (so that the code runs during class initialization)
     or a class (so that the code runs during instance construction). The switch is `-Yrepl-class-based`.
+  - every line of input is compiled separately.
+  - dependencies on previous lines are included by automatically generated imports.
+  - implicit import of `scala.Predef` can be controlled by inputting an explicit import.
+
+**Example:**
+
+    scala> import Predef.{any2stringadd => _, _}
+    import Predef.{any2stringadd=>_, _}
+
+    scala> new Object + "a string"
+    <console>:13: error: value + is not a member of Object
+           new Object + "a string"
+                      ^
+
+    scala> import Predef._
+    import Predef._
+
+    scala> new Object + "a string"
+    res1: String = java.lang.Object@787a0fd6a string
 
 ### Power Mode