About Creating Datum Planes
You can create datum planes in Style using these methods:
Create an asynchronous datum plane while creating a Style feature. This datum plane is inserted in the Model Tree before the active feature and is hidden by default.
Create a datum plane while creating a feature so that the datum plane is internal to the active feature. This internal datum plane is not seen at the top level in the Model Tree, but it is listed in the Style Tree. To create an internal datum plane, you can reference any Style entity such as Style curve endpoints, Style surface vertices, and other internal datum planes besides the regular Style references.
When creating or defining Style features, you can create datum planes as internal datum planes for the Style feature. However, you must create datum points and datum axes asynchronously. The advantage of using an internal datum plane is that it can have references to other entities in the current Style feature.
You can also edit, manipulate, or regenerate the internal datum plane.