ASA FirePOWER Module User Guide for the ASA5506-X, ASA5506H-X, ASA5506W-X, ASA5508-X, and ASA5516-X, Version 5.4.1 - Understanding and Writing Intrusion Rules [Cisco Secure Firewall ASDM] - Cisco
Figure 1 from Improvement on rules matching algorithm of snort based on dynamic adjustment | Semantic Scholar
Rule Options | Working with Snort Rules | InformIT
Comprehensive Guide on Snort (Part 1) - Hacking Articles