The rules come from the Solaris 7 regexp(5) manual page. The I2A2 reflector DBM follows these rules ... is a one-character RE that matches any character. 1.4 A non-empty string of characters enclosed ...

Regex patterns help search text strings efficiently (e.g., emails, digits, specific sequences) using symbols. Excel provides predefined regex functions (REGEXTEST, REGEXEXTRACT, REGEXREPLACE ...

Regular expressions (or REGEX) are search patterns that can be used to check if a string of text conforms to a given pattern and extract or replace strings of text that match a given pattern.