rules.json

{
    "rules": {
        ".read": true,
        ".write": true,
        "boardmetas": {
          "$boardid": {
            ".validate": "newData.hasChildren(['createdAt', 'width', 'height'])",
            "createdAt": {
              // is a number after 20150101 and before now
              ".validate": "newData.isNumber() && newData.val() > 1420099200000 && newData.val() <= now"
            },
            "width": {
              ".validate": "newData.isNumber()"
            },
            "height": {
              ".validate": "newData.isNumber()"
            },
            "thumbnail": {
              // A thumbnail is allowed, but not required
              ".validate": "newData.isString()"
            },
            "$others": {
              // disallow any other children
              ".validate": false
            }
          }
        },
        "boardsegments": {
          "$boardid": {
            "$segmentid": {
              ".validate": "newData.hasChildren(['color', 'points'])",
              // TODO: validate that color is within range -2147483648 - 2147483647
              "points": {
                "$point": {
                  ".validate": "newData.hasChildren(['x', 'y'])",
                  // validate that x and y are numeric and within the boards width and height
                  "x": {
                    ".validate": "newData.isNumber() && newData.val() >= 0 && newData.val() < root.child('boardmetas').child($boardid).child('width').val()"
                  },
                  "y": {
                    ".validate": "newData.isNumber() && newData.val() >= 0 && newData.val() < root.child('boardmetas').child($boardid).child('height').val()"
                  },
                  "$other": {
                    ".validate": false
                  }
                }
              }
            }
          }
        },
        "$others": {
          // disallow any other children
          ".validate": false
        }
    }
}