“Blender has five types of metas, each determined by its underlying (or directing) structure.”
Then underneath it listed out the five main types (Ball, Capsule, Plane, Ellipsoid and Cube). Do you know exactly what the word ‘directing’ mean in that sentence? I gather the author wanted to say,
The term “directing” is used to convey the idea that the underlying structure of a meta object determines its type. The word “directing” is synonymous with “determining” or “governing” in this context. It suggests that the structure of a meta object influences and guides its classification into one of the five types mentioned: Ball, Capsule, Plane, Ellipsoid, or Cube.
In simpler terms, the word “directing” in that sentence means that the type of a meta object in Blender is determined by its basic shape or structure. The shape of the object guides or influences its classification into one of the five types mentioned (Ball, Capsule, Plane, Ellipsoid, or Cube). So, the way the meta object is shaped determines what kind of object it is considered to be in Blender.