Of course!
The manual is a wiki, as discussed in this thread.
We try to structure the manual as a guidebook, so that it introduces high-level concepts first, then gradually builds to show the way these things are used. The DirectGui pages aren’t as good at following this plan as some of the other pages in the manual, so it wouldn’t be a bad thing at all if someone were to restructure them to at least add a place to put the overall usability information, things like “you can configure nested pieces using piecename_component = componentValue, for instance thumb_clickSound = soundFile”.
As to where this should be tweaked in the code itself, I invite you to read the code. The DirectGui code is all Python (except where it falls back to the low-level PGui implementation), and though it’s not the easiest Python code in the world to read, it’s at least internally self-consistent. You’ll see that the clickSound and rolloverSound options appear in DirectButton.py, and ‘thumb’ is a DirectButton component of DirectSlider. You’ll also see that the default sounds are read from DGG.getDefaultClickSound(), and if you follow that to its source in DirectGuiGlobals.py, you’ll see that it can also be changed globally with DGG.setDefaultClickSound().
Whether this is a good interface is subject to some debate, of course; but it would certainly be easy to change the default to silent by editing the appropriate lines in DirectGuiGlobals.py.
David