Plane objects were designed primarily to handle crystallographic planes but 
they should provide useful functionality even in the absence of 3D periodic 
objects (cells). Plane objects can own directions, atoms, orbitals and texts. 
The low-level engine infra-structure required to implement plane objects is 
fully implemented but everything else is not done yet. Plane objects must handle 
Miller and Miller-Bravais indices and all the related crystallographic relations 
provided by direct- and reciprocal-lattice representations. Users should be able 
to choose planes of atoms in cells, clusters or molecules, automatically producing 
plane objects reproducing those planes, including the atoms and its child, bonds, 
orbitals and texts, and then handle these new plane objects as totally independent 
viewing and building tools.