| `axis` | `string` | | Which type of axis this is. Possible values are: `'x'`, `'y'`. If not set, this is inferred from the first character of the ID which should be `'x'` or `'y'`.
| `offset` | `boolean` | `false` | If true, extra space is added to the both edges and the axis is scaled to fit into the chart area. This is set to `true` for a bar chart by default.