Relevant version: V9 and up
In version 9, the standard Look Ahead and Look Behind clauses are stripped from the regular expression and executed separately in Java. This significantly improves the regular expression performance. To achieve the improved performance, the look ahead and look behind sections must exactly match one of the supported standard sections. If either section differs even slightly, that section is executed as part of the regular expression without performance improvement.
The following standard sections are supported by the performance improvement:
NOTE: After adding a regular expression rule, observe the system for about one hour to ensure that the system does not slow down too much (unlikely, but possible) and that there are no unexpected false positives.
Look Ahead: (?=(?:[^-\w])|$)
Look Behind: (?<=(^|(?:[^)+\d][^-\w+]))) and (?<=(^|(?:[^)+\d][^-\w+])|\t))