What is "matches regex" for?

The abbreviation for regular expression is regex.  The process of analyzing or modifying a text with a regex is called: The regular expression is applied to the text/string. The pattern defined by the regex is applied on the text from left to right. Once a source character has been used in a match, it cannot be reused.

The "matches regex" option allows you to implement regular expressions in Google Tag Manager for matching text patterns. Regex is useful for expressing more complex types of rules such as "fire the tag when the URL starts with A and ends in B or C."...