Returns number of unique values of an integer or string attribute.
op:/ syntax can be used to refer to a SOP operator rather than a file on disk.
What type of attribute data to fetch.
The file on disk to fetch an attribute from.
Attributes can be stored on points, vertices, primitives, or even as global attributes (Detail). The class refers to where to look for it. It will adjust the meaning of Point or Primitive and Vertex.
The name of the attribute to fetch.
id fetches the common id attribute, and
name will fetch the name.