add a way to indicate when a point is off the scale

New feature request: it would be great if there were a way to hint when a point is off the scale.

• With bars, it's already possible - the top of the bar has no border. However, this is quite subtle, and perhaps it could be made more obvious that it's truncated, e.g. by making the top few mm of the left and right edges end with dashes and an arrow-tip.
• With bubbles/scatter points (that are not connected by lines), there is no way to see that a bubble is too high (rather than being omitted because the point is null).
• This is particularly problematic when the user has manually set the y-axis range, and has cut off a point. (in auto-range mode, points are never missed out).

This might be indicated by showing a "^" at the top of the paper pointing to where the point would be. (such a symbol should also get the hover-text of the associated point).

These indicators should be dynamic - as the axis is zoomed and scrolled. Maybe we need a pref (default on) to turn this off?

Thanks for your consideration - I hope the idea is useful.

Issue 中没有指定文件或测试。首先沿着 bar 和 scatter/bubble 的渲染路径，以及坐标轴缩放和滚动更新进行追踪；当被裁剪的点具有清晰、动态的指示器和关联的 hover 文本，同时 null 点仍然能够区分时，即表示完成。