def key=(key)
      raise(ArgumentError, "keys must be convertible to Symbol; was: #{type.class.name}.") unless type.respond_to?(:to_sym)

      unless bibliography.nil?
        bibliography.strings.delete(@key)
        bibliography.strings[key.to_sym] = self
      end

      @key = key.to_sym
    end
def key=(key)
      raise(ArgumentError, "keys must be convertible to Symbol; was: #{type.class.name}.") unless type.respond_to?(:to_sym)

      unless bibliography.nil?
        bibliography.strings.delete(@key)
        bibliography.strings[key.to_sym] = self
      end

      @key = key.to_sym
    end
Creates a new instance.
 Sets the string's key (i.e., the symbol identifying the constant).