SExpandableArea

    "SExpandableArea": {
        "Aka": "expandable_area",
        "BorderImage": {
            "Style": "FEditorStyle",
            "Brush": "DetailsView.CategoryTop"
        },
        "BodyBorderImage": {
            "Style": "FAppStyle",
            "Brush": "Brushes.Recessed"
        },
        "Padding": 4,
        "HeaderPadding": [5, 3],
        "AllowAnimatedTransition": true,
        "InitiallyCollapsed": false,
        "OnAreaExpansionChanged": "print('OnAreaExpansionChanged text: {}'.format(%))",
        "HeaderContent": {
            "STextBlock": {
                "Text": "Some Head Text"
            }
        },

        "BodyContent": {
            "SHorizontalBox": {
                "Slots": [
                    {
                        "STextBlock": {
                            "Text": "Some Body Text"
                        }
                    },
                    {
                        "AutoWidth": true,
                        "SButton": {
                            "Text": "Some Button In Body Content",
                            "OnClick": "sketch.data.set_is_expanded('expandable_area', False, True)"
                        }
                    }
                ]
            }
        }
    }