how to define/extend the foldable()

Hi I am looking for way to extend the Fold foldable() but could not find any example online.
Can someone help?

The docs tell you you can use the foldServide facet or add a node prop to your syntax tree.

So my problem is, I don’t know how to register a servive to foldService. In my use case, i cannot use node prop. I added extension for decoration before following some examples. But could not find anything for fold. Pls help. Thanks.

Turn out it is very simple. Note it down here in case someone is also looking for this.
Just need to add the following line to the extension array: