Names prefixed with 'Na_' are offset constants used
to index into sub-elements of NuGraf arrays. For example, the predefined constants Na_RED,
Na_GREEN and Na_BLUE are used to index into the red,
green and blue color components of the Nd_Color abstract data type. Usage
of these constants also reduce programming error, as well as increasing the portability
and readability of the resulting NuGraf program.
