# v4.4.18 ## Enhancements - Improved the placeholder syntax of the rule engine [#10470](https://github.com/emqx/emqx/pull/10470). The parameters of certain actions support using placeholder syntax to dynamically fill in the content of strings. The format of the placeholder syntax is `${key}`. Prior to the improvement, the `key` in `${key}` could only contain letters, numbers, and underscores. Now the `key` supports any UTF8 character after the improvement. ## Bug fixes