Some implementation also allow mode to be change during a regex or applied on part of a regex. The (?modifier) and (?-modifier) may be use inside a regex to switch modes  on and off respectively (ie. /SenSiTiVe Text(?i)insensitive text(?-i)Back To Sensitive Text/). You can also apply a modifier to a subexpression using (?modifier:…) like in SenSiTiVe Text(?i:insensitive text)Back To Sensitive Text/.