# File lib/vpim/field.rb, line 546
      def pvalue_iadd(pname, pvalue)
        pname = pname.upcase

        # Get a uniq set, where strings are compared case-insensitively.
        values = [ pvalue, @params[pname] ].flatten.compact
        values = values.collect do |v|
          if v.respond_to? :to_str
            v = v.to_str.upcase
          end
          v
        end
        values.uniq!

        h = @params.dup

        h[pname] = values

        mutate(@group, @name, h, @value)
        values
      end