## Data Definition


#### Label
Type: `string`

Default validate:  
```js
function (d) { return true; }
```

Default accessor:  
```js
function (line) { return String(line[0]); }
```

#### Value
Type: `number`

Default validate:  
```js
function (d) { return !isNaN(this.accessor(d)); }
```

Default accessor:  
```js
function (line) { return Number(line[1]); }
```