zBone
-----
This node specifies bone-specific attributes.

+--------------------------+--------------------------------------------------------------------------------+
| Attribute                | Meaning                                                                        |
|                          |                                                                                | 
+==========================+================================================================================+
| **enable**               | When disabled, removes this bone and affiliated attachments from the solve.    |       
+--------------------------+--------------------------------------------------------------------------------+
| **collisions**           | Vertices from tissues that intersect this bone (provided this bone is a closed |
|                          | volume and not self-intersecting) will be pushed out.                          |
+--------------------------+--------------------------------------------------------------------------------+
| **collisionVolume**      | Vertices from tissues that intersect this bone (provided this bone is a closed |
|                          | volume and not self-intersecting) will be pushed out.                          |     
+--------------------------+--------------------------------------------------------------------------------+
| **hardContact**          | When enabled, uses implicit hard contact forces - this is more numerically     |
|                          | stable but comes at the cost of a slower solve.                                |      
+--------------------------+--------------------------------------------------------------------------------+
| **contactStiffness**     | The stiffness of “softContact” springs. It controls the “hardness” of the      |
|                          | contact between the two objects. Lower values may cause intersections to occur |
|                          | during contact, but will be more stable. Higher values will cause little or no |
|                          | intersection, but may require “hardContact” to be enabled and/or more solver   |
|                          | substeps to be stable.                                                         |
+--------------------------+--------------------------------------------------------------------------------+
| **contactStiffnessExp**  | The power to which the value of the **“contactStiffness”** is raised.          |
+--------------------------+--------------------------------------------------------------------------------+
| **contactSliding**       | When enabled, contacts are resolved with the freedom to slide tangentially.    |
+--------------------------+--------------------------------------------------------------------------------+