[Lazarus] unit Dialogs and showmessage

[Bernd]

http://lazarus-ccr.sourceforge.net/docs/lcl/dialogs/showmessage.html

Source position: dialogs.pp line 510

procedure ShowMessage(
  const aMsg: String
);

there is also an example program:

Program LazMessage;
 Uses Dialogs;
 begin
   ShowMessage ('This is a message from Lazarus')
 end.

This does not compile: project1.lpr(4,16) Error: Identifier not found
"ShowMessage"

Also i cannot find the definition of this procedure anywhere in the
unit dialogs and also this file is called dialogs.pas and not
dialogs.pp on my system. How would i tell the use clause that i would
like to use dialogs.pp instead of dialogs.pas?

I am on linux, using fpc 2.4 and a few days old lazarus snapshot. Does
this unit or this function not exist on other platforms than windows?
There is no mention of this in the documentation, or is the
documentation outdated or am i doing/understanding some completely
wrong here?