[LSC] BFC Standard - Revision 1

[William Howard]

> On the matter of culling parts even if the super-file isn't certified ...
Thinking some more about this, this *has* to be incorrect.  If it was
correct that you can't BFC a subfile unless the superfile is certified,
hardly any models would ever be rendered with  culling applied as the main
model file is almost never BFC certified. 

I was thinking that perhaps the criterion is if the superfile contains
polygons, but that also can't be true as some of my model files contain raw
rects and tris to create arrows (and they render correctly in LDView which
Travis says performs back face culling regardless).

So, we seem to have a case that back face culling can be applied if the main
model file or a part file within a superfile is certified.

The problem seems to be with the definition of the term "current reference
branch" - which is used in the definition of culling (under Language
Extension Functionality) but never defined itself.

(The terms "file-reference tree", "file-reference branch" also need sorting
out)