Function run_to 

pub fn run_to(
    argv: impl IntoIterator<Item = String>,
    out: &mut dyn Write,
) -> Result<(), String>

The same dispatch as run, against an explicit sink. 与 run 相同的分发，但写到显式指定的输出。

The operator commands (check --json, explain, grafts) exist to be read by a machine, so their document has to be assertable without redirecting the process’s stdout from a test: this entry point is what the tests drive. 操作命令（check --json、explain、grafts）存在的意义就是被机器读取，因此它们 的文档必须能在不重定向进程 stdout 的情况下被测试断言：测试驱动的就是这个入口。