Thymeleaf - how to add a custom util?

Thymeleaf has a number of useful Utils like #strings.capitalize(...) or #lists.isEmpty(...). Trying to add a custom one but have no idea how to register this.

Have made a custom Util class:

public class LabelUtil {

    public String[] splitDoubleWord(String str) {
        return str.split("[A-Z]", 1);
    }
}

Now I'm going to use it like this:

<span th:each="item : ${#labels.splitDoubleWord(name)}" th:text="${item}"></span>

Of course, it won't work due I haven't registered the Util and defined #labels var.

So, the question is how and where to?