php怎么从json文件读出特殊节点的值

{
        "condition2": {
            "name": "条件2",
            "datatime": {
                "start": "2021-01-10",
                "end": "2021-01-15"
            },
            "cameras": ["cam1"],
            "site": [{
                "category": "People count",
                "contents": {
                    "active": ["Pie/Line/Bar/Table chart"],
                    "Pie/Line/Bar/Table chart": {
                        "chart type": {
                            "Line graph (x:time, y:count)": 0,
                            "Table": 0,
                            "Number of count": 0,
                            "Bar graph (x:time, y:count)": [0, 0],
                            "Bar graph (x:camera, y:count)": 0,
                            "Pie chart(Occupancy)": [5, 5]
                        },
                        "contents": {
                            "select": 1
                        }
                    },
                    "Heat map":{
                        "show one heatmap": 0
                    },
                    "Still image": {
                        "select": 0
                    }
                }        
            }]
        },
}

怎么从Php读出节点："Heat map"，"Still image"，"Pie/Line/Bar/Table chart"等的内容。（节点名字中有空格或特殊字符）
php添加或删除某一节点可以吗

$data['condition2']['site'][0]['contents']['Heat map']