坐标轴可以画在绘制区域

# 坐标轴灵活布局

希望坐标轴可以画在如下图蓝色位置。


## 实现思路

坐标轴也是一种 Mark，这里和 ruleX 很像。可以通过设置 position 来指定绘制区域。

```js
G2.render({
type: 'point',
axis: {
y: {
position: 'plot', // 在 plot 区域绘制
x: [3], // 数据驱动的位置
},
},
});
```

Start by tracing how axes are represented as Marks and how ruleX handles positioning, then inspect the position API shown in the example. Done means an axis can render inside the plot region at a data-driven coordinate while existing axis layouts continue to work.

Written by the indexing model from the issue text.