rl.cursor
相对于 rl.line 的光标位置。
当从 TTY 流读取输入时，这将跟踪当前光标在输入字符串中的位置。 光标的位置决定了在处理输入时将被修改的输入字符串部分，以及将呈现终端插入符号的列。
The cursor position relative to rl.line.
This will track where the current cursor lands in the input string, when reading input from a TTY stream. The position of cursor determines the portion of the input string that will be modified as input is processed, as well as the column where the terminal caret will be rendered.