[Lazarus] Message Loop paused when no interaction with mouse?

[Bernd]

2011/4/20 Henry Vermaak <henry.vermaak at gmail.com>:

> As I've noted before, PostMessage does wake up the main thread

In which Unit is PostMessage() defined, and also is there some
documentation about

procedure ...; message ...;

somewhere, because I can't find anything. Is this an FPC thing
(because of the procedure decoration) or is PostMessge() something LCL
related and has nothing to do with the message keyword?