This is correct. According to this article[0], posted in another comment[1], iOS 9's content blocker regular expressions are limited to a subset of regex for wh

This is correct. According to this article[0], posted in another comment[1], iOS 9's content blocker regular expressions are limited to a subset of regex for which matching can be done in linear time: "Extremely powerful, regular expressions can surprisingly be done in linear time if you use a strict set of regular expression characters through Thompson’s NFA algorithm. Safari’s Content Blocker implementation in fact imposes this strict regular expression limitation ..." 0. http://blog.appgrounds.com/content-blockers-beat-adblocking/ http://blog.appgrounds.com/content-blockers-beat-adblocking/ 1. https://news.ycombinator.com/item?id=10192562 https://news.ycombinator.com/item?id=10192562