Each Production has the form
N = E . where means "an N is defined to be a E"
E is an expression which may contain the following operators:
X | Y means "either an X or a Y"
[ X ] means 0 or 1 occurrence(s) of an X"
{ X } means "0 or more occurrences of an X"
also
( ) group sub-expressions
" " enclose a terminal symbol