That's a nice fact to know, that F5 is the Refresh Desktop key in Xfce. I don't find it documented anywhere and, being obscure, is fairly useless if the operator doesn't know about it. So we could prominently document the uses of function keys, F5 in particular. Or we could put the Refresh Desktop command where people expect to find it, in the Desktop context menu. I suggest both.
You can find a list of preassigned keyboard shortcuts in the Desktop menu ("start" menu), Settings, Window Manager settings, keyboard tab, Window Shortcuts. There are bunches of them. I was particularly happy to find Control-Alt-d, which toggles minimizing all windows or returning them to their positions before minimizing. I was able to ditch the Show Desktop icon in the panel, giving me more room for other stuff. You can customize the keyboard shortcuts by clicking on the plus sign for Add and giving your new shortcut set a name. The default shortcuts will be copied into the new set. To change a shortcut, double-click on it and hit the key combination you want to use when the Compose Shortcut box comes up.
Interestingly, F5 for Refresh Desktop doesn't appear in the list. I didn't know F5 would do that. I think Control-R might refresh the desktop, too, according to an Arch forum message I found through Google. I've never needed to refresh the desktop, so I never looked to find out how to do that.
As an operator/user, when I look at VL SOHO, I don't see VL and KDE as separate entities. Likewise, VL Std wrt Xfce. So when I right-click the Desktop and select Refresh Desktop from the context menu, I'm unconcerned whether this is a KDE or Xfce command. [Therefore, the Refresh Desktop command is "available in VL 5.8 SOHO."]
You may not see KDE or XFce as separate from VL, but they most certainly are. Unlike MS Windows, the desktop you see in Linux is a matter of your own choice and you don't have to use a desktop at all. Think back to Windows 3.1 days. Windows was just another application running on MS-DOS. You could close down Windows and operate in a pure DOS environment. That's how the desktop is in Linux. If you close down X, you're at a pure command line system.
VL Standard and SOHO come with default desktop environments as a convenience to users. You don't *have to* use XFce with Standard. You can use any of the window managers in the repository and if you want one that isn't there, you can either find a Slackware package for it or compile it yourself. Likewise with SOHO. You can install and use XFce if you prefer, or IceWM, or Fluxbox, or any of numerous others. You will have a rude awakening if you think all the same commands that work in KDE will work in any other window manager you may use instead of KDE.