- The list box is separate to the window in Spy++ so its not contained in the window.
So the app frame perhaps isnt passing everything to all open windows. What happens if you have two of the same windows open, do both fail, one work one fail, or both work?
So WM_xyz are Windows Messages sometimes with extra parameters which could be an address to a struct that contains more information.
The Accept loop in Clarion is the Message Loop in this document, basically windows is an (OS) Loop with one or more (program) loops and a program window is a (procedure) Loop usually on its own thread, but not always.
Window Messages (Get Started with Win32 and C++) - Win32 apps | Microsoft Docs
So Loop based OS’s have the advantage they can recover from crashes better than the older punch card and early main frame systems which would just crash and hang once some code has executed and/or hit a problem. The Windows core is reportedly one of the smallest loops for an OS, but that could just be MS marketing speak, but then the OS Tiny-Os, its core is only 400bytes according to this doc and many applications fit within 16Kb of memory, which is tiny with todays standards, you could fit an OS inside a hard disk controller or something like that, or some of todays digital watches!
Unbekannt (berkeley.edu)
These are some of the messages explained
WM_PAINT message (Winuser.h) - Win32 apps | Microsoft Docs
WM_ERASEBKGND message (Winuser.h) - Win32 apps | Microsoft Docs
WM_CTLCOLORSCROLLBAR message (Winuser.h) - Win32 apps | Microsoft Docs
The Spy++ is just showing you some of the WM its seeing, probably by hooking into the app, but this may become rarer as windows security is locking down some things which could be done easily in XP days.
API monitor apps also exist which will give you more of a trace of whats going on, one I’ved used in the past which OSS is rohitab.com api monitor, you can see what order some things are happening, like you can monitor how the Clarion runtime works.
Now if you are in Europe, and you find a bug, you can legally reverse engineer other peoples code to fix bugs. Now what the legal system doesnt comment on is what other knowledge you might gain in that process of reverse engineering and fixing bugs, buts its legal here in Europe, the High court has recently ruled on it!