instance method cut_excerpt_part

# File actionview/lib/action_view/helpers/text_helper.rb, line 464
        def cut_excerpt_part(part_position, part, separator, options)
          return "", "" unless part

          radius   = options.fetch(:radius, 100)
          omission = options.fetch(:omission, "...")

          part = part.split(separator)
          part.delete("")
          affix = part.size > radius ? omission : ""

          part = if part_position == :first
            drop_index = [part.length - radius, 0].max
            part.drop(drop_index)
          else
            part.first(radius)
          end

          return affix, part.join(separator)
        end