The charge production sets the charge attribute of a bracket atom. This non-terminal begins with either the plus or minus terminals ("+" and "-" respectively) and ends with an optional nonzero non-terminal that sets the charge multiplicity. A plus terminal ("+") followed by anything other than a nonzero digit sets the charge attribute to one. Likewise, a minus terminal ("-") followed by any character other than a nonzero digit sets the charge attribute to minus one. Charge values of zero are obtained by omitting the charge production.