ddoc doesn't generate entries of function without any comments?

[Flamaros]

I need dig into some low level APIs regularly. Modules like 
std.c.window and std.c.linux doesn't have any documentation about 
what it's contains.

I also try to generate some docs with ddoc on my project and it 
seems it doesn't create any functions/methods entries if there is 
no description on those.

Is there any reason for that?

Generally a function without any description can be considered as 
unstable, but maybe the visibility have to play a role here?