http://www.rfc-editor.org/rfc/rfc7034.txt
RFC 7034: HTTP Header Field X-Frame-Options, D. Ross, T. Gondrom2013-10-01T23:00:00-00:00To improve the protection of web applications against clickjacking, this document describes the X-Frame-Options HTTP header field, which declares a policy, communicated from the server to the client browser, regarding whether the browser may display the transmitted content in frames that are part of other web pages.