sentences:  Google observes Internet standard mechanisms for requesting that caching be disabled via the robots.txt file, which is another mechanism that allows operators of a website to request that part or all of their site not be included in search engine results, or via META tags, which allow a content editor to specify whether a document can be crawled or archived, or whether the links on the document can be followed.The U.S. District Court of Nevada ruled that Google's caches do not constitute copyright infringement under American law in "Field v. Google" and "Parker v. Google".On February 20, 2017, Google agreed to a voluntary United Kingdom code of practice obligating it to demote links to copyright-infringing content in its search results.