The Regex Field Replacement index stage lets you match against a source field and append or overwrite that field or another one with a replacement string. It uses the
One notable feature is support for flags in the prefix of the pattern, such as (?iu)\w+ where the i flag means case-insensitive and u means Unicode-aware case folding. You can also configure the desired behavior when there is no match. Additionally, you can use capture groups in your replacement configuration using $1 to denote the first capture group.
When entering configuration values in the UI, use unescaped characters, such as \t for the tab character. When entering configuration values in the API, use escaped characters, such as \\t for the tab character.