Creative ZEN (2Gb, tester's unit P)
1 Unplug external power
2 Go to Settings, General Settings, Display, LCD Settings, No Backlight on Selected Actions
3 Select Off (changes to On)
4 Under Settings, select Volume, Play, Seek, Skip (each changes to show a + to left)
5 On Now Playing, wait until backlight goes out
6 Do Volume up/down, Play, Seek right, Skip right (Seek left and Skip left are non-operative)
7 Verify backlight does not engage.
8 Go to Settings, General Settings, Display, LCD Settings, No Backlight on Selected Actions, Settings
9 Select 'Disable on External Power' ("When plugged goes back to regular behavior")
10 Plug-in external power
11 On Now Playing, wait until backlight goes out
12 Do Volume up/down, Play, Seek right, Skip right (Seek left and Skip left are non-operative)
13 Verify backlight does engage.
This omits Disable Unknown ("Unknown actions will not turn on the backlight") because I don't know what constitutes an Unknown action.
This omits Selective Softlock and Softlock Options because TMK (in absence of a Rockbox manual for this model) this model does not have a softlock and none is mentioned in the Rockbox manual for another model https://download.rockbox.org/manual/rockbox-sansaclipplus.pdf
I suggest the UI labelling could be made a lot more comprehensible. For example, I suggest the Settings mutually exclusive commands Off (that turns the feature on) and On (that turns the feature off) would be better replaced by an On command that turns the feature on and an Off command that turns it off, with a suffixed asterisk on whichever was in effect.