# File lib/yell/formatter.rb, line 159
      def initialize( pattern = nil, date_pattern = nil, &block )
        @modifier = Modifier.new

        @pattern = case pattern
        when false then Yell::NoFormat
        when nil then Yell::DefaultFormat
        else pattern
        end.dup

        @pattern << "\n" unless @pattern[-1] == ?\n # add newline if not present
        @date_pattern = date_pattern || :iso8601

        block.call(self) if block
      end