why using bone layer without any bone?

[Hamedss]

Hi.
I'm going through the Moho library that is very interesting and brings me a lot of idea and challenging myself. In one of moho 13 characters named Mohony I see a lot of bone layers that are sub layers of character main bone layer.
for example every hand switch(HAND_A) sub layers ( or child layers) consist of vector and few bones to animate switch sub layer separately . that is very nice idea and set more freedom for animator.
but i see a lot of bone sub layers (ARM_A, FACE , BROW_A ,...) that have no bones. why?

[slowtiger]

This might have been done in Moho Debut, which doesn't have group layers, but you can as well use bone layers instead.

[Hamedss]

no. it has group masking too.
also i am wondering about 2 little fixed bone at knees and elbows. what are they doing there?The reds!

[synthsin75]

Maybe hidden bones that are controlled by smart bones in a parent bone layer?