def links_for(page)
      page.domain_aliases = domain_aliases
      @focus_crawl_block.nil? ? page.links : @focus_crawl_block.call(page)
    end
def links_for(page)
      page.domain_aliases = domain_aliases
      @focus_crawl_block.nil? ? page.links : @focus_crawl_block.call(page)
    end
It extracts URLs from the page