Class identity. Basic type.

 Every class has a unique identity, derived from the classvolume
 identity and the class index.

 A class is described by classdefinition objects in a class volume. These
 objects has specific object identities, which is specified by the vid, cix,
 bix and aix.

 The figure above describes an objid for classdefinition objects. The black fields
 must have the values specified in the figure, the gray fields are reserved
 for future use.

vid

 The volume identity of the class volume where the class i defined. Only the
 two lower entities of the volume identity can be used.

cix

 The index of the class within the class volume. The cix consists of 12 bits
 which implies that the a class can have an index in the interval [1,4095].

bix

 The index of a body within a class.
   0     The class itself, i.e. the ClassDef object).
   1     RtBody or SysBody.
   2     DevBody.
   3-6   Reserved for future use.
   7     Template object.

aix

 Index for an attribute within a body. The aix consists of 12 bits, which
 implies that each body in a class can have attributes with index in the
 interval [1,4095]

ClassId

 The classid is a 32-bit reduction of the 64-bit object identity of the
 ClassDef object for the class. It contains the vid and the cix of the class.

c-binding

 The classid is defined with a #define statement of type pwr_cClass_
 in the struct file for the class and the classvolume.
 System classes also has an enum pwr_eClass_ declared in pwr_class.h