Translations:Help:CirrusSearch/60/en


 * and
 * These run Regular expressions against the page source. They aren't efficient and we only allow a few of them to run at a time on the search cluster, but they are very powerful.  This [http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-regexp-query.html#regexp-syntax link] contains an explanation of the syntax and this [http://lucene.apache.org/core/4_8_1/core/org/apache/lucene/util/automaton/RegExp.html link] contains an actual grammar for the regex language. The version with the extra   runs the expression case insensitive and is even more inefficient.