// this tag may have values: all, noindex, nofollow, noarchive, nosnippet, noodp, notranslate, noimageindex, unavailable_after, none; see https://developers.google.com/webmasters/control-crawl-index/docs/robots_meta_tag?hl=de
if(x_robots_tag.indexOf("all",0)>=0)b+=1<<8;// set bit 8
if(x_robots_tag.indexOf("noindex",0)>=0||x_robots_tag.indexOf("none",0)>=0)b+=1<<9;// set bit 9