    # File lib/rmail/header.rb, line 357
        def add(name, value, index = nil, params = nil)
          value = value.to_str
          if params
            value = value.dup
            sep = "; "
            params.each do |n, v|
              value << sep
              value << n.to_s
              value << '='
              v = v.to_s
              if v =~ /^\w+$/
                value << v
              else
                value << '"'
                value << v
                value << '"'
              end
            end
          end
          field = Field.new(name, value)
          index ||= @fields.length
          @fields[index, 0] = field
          self
        end