To control the angular dimensions of a family, apply a labelled angular dimension to a reference line.
Unlike reference planes (with infinite extents), a reference line has specific start and end points and can be used to control the angular constraints within components such as a web truss, a door with an instance door swing, or an elbow.
Loaded door family with an angular dimensioned reference line
To add and dimension a reference line
This is known as flexing the model. It is important to make sure the reference line adjusts as expected before adding model geometry to it.
To add and align model geometry to a reference line
The geometry moves with the reference line as the angle changes.