# File lib/nanoc/extra/link_collector.rb, line 23
    def filenames_per_href
      require 'nokogiri'
      filenames_per_href = {}
      @filenames.each do |filename|
        hrefs_in_file(filename).each do |href|
          filenames_per_href[href] ||= Set.new
          filenames_per_href[href] << filename
        end
      end
      filenames_per_href
    end