Returns the name of the class of an object passed as the first argument.

\gdlkeyworddesc{SUPERCLASS}
Returns instead an array of all direct superclasses of the object
  passed as the first argument.
In this case the first argument may be a string defining the object name. 

\gdlkeyworddesc{COUNT}
Allows to pass a reference to a variable into which the number of direct
  superclasses will be stored.

\gdlcodeexample{obj_class_0}{obj_class,count,/superclass}{}

A list of all known classes is returned if called without any argument:
\gdlcodeexample{obj_class_1}{obj_class}{}
