Used for: converting a list to a normal text field with the list elements separated by a specific character (e.g. comma).
This rule is the opposite of the split text to list rule. In this case your field already contains a list and you want to convert this to a normal text field (with the elements separated by a certain character). In the example below we convert a list of sizes to a text field with the sizes separated by "-".
The effect of this rule is shown in the screenshot below: