How to print unicode characters (no library)?

Mon Dec 27 07:29:05 UTC 2021

On Sunday, 26 December 2021 at 23:57:47 UTC, H. S. Teoh wrote:
> In some Unix terminals, backspace + '_' causes a character to 
> be underlined. So it's really a mini VM, not just pure data. So 
> yeah, the good ole ASCII days never happened. :-D
>
>
> T
>
How can you do that? I'm trying to print the codes for them but 
it doesn't work. Or you cannot choose to have this behavior and 
there are only some terminals that support this?