How can you properly use Regular Expression (RegEx) table variables in GTM?

Regular Expression (RegEx) table variables in Google Tag Manager (GTM) are used to map values based on regular expression matching. They take an input value, compare it against a series of regular expressions defined in the table, and return a corresponding output value when a match is found. To properly use a RegEx table variable, first define the input variable. This is the variable whose value will be tested against the regular expressions. Next, create the RegEx table. The table consists of rows, each containing a regular expression and a corresponding output value. When GTM evaluates the RegEx table variable, it iterates through each row, comparing the input value against the regular expression in that row. The regular expressions are evaluated in the order they appear in the table. The first regular expression that matches the input value will determine the output value. It's crucial to construct your regular expressions carefully to ensure they match the intended values and avoid unintended matches. Use RegEx syntax that's appropriate for your use case. GTM uses JavaScript-style regular expressions. Always use the most specific RegEx possible to avoid unintended results, and to improve performance. You can specify a default value to be returned if none of the regular expressions match the input value. The default value is set in the variable configuration. If no default value is set, the RegEx table variable will return 'undefined' if no match is found. A common use case is categorizing URLs based on patterns. For instance, you might want to categorize URLs containing '/blog/' as 'Blog' and URLs containing '/product/' as 'Product'. Your RegEx table would have rows with the RegEx '^/blog/.*$' mapping to 'Blog' and '^/product/.*$' mapping to 'Product'. The input variable would be the 'Page URL' variable. It is important to enable 'Full RegEx matching' in the variable configuration to ensure that the RegEx is matched against the entire input string. Otherwise, a partial match will be considered a successful match. RegEx table variables can be used for more complex transformations involving capturing groups. Capture groups allow you to extract portions of the matched input string and use them in the output value. To use capturing groups, include parentheses in your regular expression to define the groups. In the output value, use '$1', '$2', etc., to refer to the captured groups. For instance, if you want to extract the product ID from a URL like '/product/12345', your RegEx could be '^/product/(.*)$', and your output value could be '$1'.