The first feature you create in the model can be a solid or surface, datum, or a group of features copied from your UDF (User-Defined Feature) library.

The first feature is the working block of material that is refined and modified until the final design. The first feature extrusions are always extruded in the positive direction (out of the screen towards you).

You can create a group from your UDF library as the base feature as long as it has no references to other features.

For example, you might have a UDF that is a solid feature that references two datum planes, which reference the default coordinate system (created as the base feature). All the features must then be included in the UDF to become the base feature for a new part.