If you turn this on, then the variable dropdown list allows users to select multiple options at the same time. For more information, refer to [Formatting multi-value variables]({{< relref "formatting-multi-value-variables/" >}}).
By default the `All` value includes all options in combined expression. This can become very long and can have performance problems. Sometimes it can be better to specify a custom all value, like a wildcard regex.
In order to have custom regex, globs, or lucene syntax in the **Custom all value** option, it is never escaped so you will have to think about what is a valid value for your data source.
