The ``Dimension'' property is an unsigned integer representing
the dimensionality of the co-ordinates. This has the default value
zero, for unknown or no coordinates, 2 for 2-dimensional co-ordinates
(such as depictions) and 3 for 3-dimensional co-ordinates. This
property is typically set by the file format reader indicating the
dimensionality of the input file (0 for SMILES, 3 for MOL2 and 2 or 3
for MDL SD files etc...)