path对象的viewBox怎么定义？

看到属性列表里面有viewBox (string) 不过不知道这个东西怎么定义，例子里面也没有。。。
根据SVG文档的话是 `x y width height`不知道是否只是照着SVG原生的？

个人感觉既然语言支持，大概specify成一种新的对象比较好？比如一种 `box (x, y, w, h)` 还可以用于别的东西？

The issue does not name any files, tests, or entry points. First clarify how the path object's viewBox should follow SVG's x y width height convention, then determine whether a reusable box object is part of the language design; done means the semantics and supported syntax are decided and documented with an example.

Written by the indexing model from the issue text.