We don't have any docs for BCON.

http://mongoc.org/libbson/current/creating.html#simplified-bson-c-object-notation
http://mongoc.org/libbson/current/json.html
http://mongoc.org/libbson/current/parsing.html#finding-fields-using-dot-notation

This is the only docs we have for BCON :|

We may want to look into documenting the macros with they respective bson_append_.. docs:
https://github.com/mongodb/libbson/blob/master/src/bson/bcon.c#L214-L292