Regular Expressions in SNiFF+

Introduction
Regular expressions (regex) are a powerful means to specify patterns for filters and search strings in the various SNiFF+ tools. The syntax conforms largely to the GNU regular expression syntax used in the Emacs editor, with some SNiFF+ specific enhancements.
Basically, regular expressions are a system of matching character patterns. How you use regular expressions depends on what you need. This introduction to regular expressions, following the Quick Reference - Syntax table, groups regular expression usage by functionality.
Quick Reference - Syntax
Literals and metacharacters
Escape character -- backslash (\)
Do not match -- exclamation point (!) (in SNiFF+)
Single character wild card -- period (.)
Quantifiers -- how often to match
Position -- where to match
Nonprinting or whitespace characters
Character classes or lists
Choosing from a range of alphanumeric characters
Excluding a character list
Metacharacters inside square brackets
Special character classes in SNiFF+
Example
Groups, alternatives and back references
Examples