Netbeans GUI builder - custom class properties category

Question

I want to know how to categorize the properties of my custom JComponent in the netbeans GUI properties editor.

so anyways. There is a property "key" in there and it is under the category "other properties". How would I make a new property category for it so it is under a category for example "Special properties"?

The code in question is like this:

public void setKey(String ke) {
    //functionality
}

public String getKey() {
    return k.getText();
}

I know this is possible. I saw such a feature somewhere a long time ago but I cannot find it back.