def to_html(input, context = {}, result = nil)
      result = call(input, context, result = nil)
      output = result[:output]
      if output.respond_to?(:to_html)
        output.to_html
      else
        output.to_s
      end
    end
def to_html(input, context = {}, result = nil)
      result = call(input, context, result = nil)
      output = result[:output]
      if output.respond_to?(:to_html)
        output.to_html
      else
        output.to_s
      end
    end
Like call but guarantee the value returned is a string of HTML markup.