The ACS_ characters are for box drawing, mainly. The division into “main” and 
“alternate” character sets is just for historical reasons, like a lot of things 
in curses. On an old VT100 terminal, you'd send a special code to switch 
between the modes. So now, when you want curses to draw the upper left corner 
of a box -- on any terminal -- you can just addch ACS_ULCORNER, instead of 
worrying about the terminal-specific way to get that. And yes, this whole thing 
is semi-obsolete in the Unicode era. But as an implementer, you still need to 
make that map, so old code will work.

I hope this helps. I must admit I'm not entirely sure what you're asking for.

From: anatoly techtonik
Sent: ‎Sunday‎, ‎April‎ ‎12‎, ‎2015 ‎4‎:‎35‎ ‎AM

To make it more clear, I am trying to decouple the logic in port implementation 
from C semantics to understand how PDCurses work, and so far the mapping of 
ACS_ macros and its purpose is not very clear. The guide say what should be 
done in ports, but it is still not clear why it is needed and what should 
happen between PDCurses and Operating System.

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