Actually this is all getting rather silly and FWIW I believe the SA CAA are wrong here. 'M' would appear to be:
1. Unlit
2. Narrow - Charlie210, who's post has been 'removed' by some helpful person told us both of these.
3. For access to Apron M
and probably a 'taxilane'
but whether in fact it quacks or not, or whether it is a lane or taxiway is not particularly relevant except to explain why the 'width of taxiways' is stated at 30.5m when 'M' is less, and why the SA CAA themselves appear to refer to it as a taxilane on the chart. In my experience, airports are full of unlit narrow tarmac surfaced routes crossing and joining taxiways.
There are other ducks to pluck here, are there not?