netgraph: documentation issue? What kernel options? Where to find?

For a small SoC based system, I use a highly customised static kernel and build the
system via NanoBSD with no kernel modules.

Tyring to track down some network issues with recent CURRENT I figured out, that when
using the ppp client to connect via modem to the ISP and there is no 

options	NETGRAPH_ETHER
options	NETGRAPH_PPPOE

in the kernel configuration, the resulting system fails to establish a ppp session. The
man page states, that a netgraph node is established, but as hard as I look, I can not
find any(!) information in the man pages what options are necessary/optional to provide
the correct module statically.

The same is for many other NETGRAPH_XXX features. Starting from man page "man 4
netgraph", section "SEE ALSO", I started tweaking the kernel with NETGRAPH_XXX, i.e.
ng_vlan -> NETGRAPH_VLAN until the compiler bails out with an error, for instance
ng_car -> NETGRAPH_CAR.

I tried to find out what options cover which netgraph module but there is - right,
nothing I can find on a direct route.

Since netgraph isn't so brand new (I guess ~ 2000 from the PDFs I found on the network),
there must be some documentation other than "reading the source code".

Please give me some hints where to find the entry point for the appropriate documented
options for netgraph modules.

Obviously, some ng_xxx modules are prerequisite for some services to work properly, as
ppp - but I can't find any hints for "options NETGRAPH_ETHER" or "options NETGRAPH_PPPOE"
in the manpages (looked at ppp, pppoed). 

Thanks in advance,
kind regards

Oliver