[Tutor] Why does using "window.addchr()" to place a character at the lower right corner raise an exception?

[boB Stepp]

Under https://docs.python.org/3/library/curses.html#window-objects in
the curses docs, it states:

<quote>
window.addch(ch[, attr])
window.addch(y, x, ch[, attr])
[...]

Note

Writing outside the window, subwindow, or pad raises a curses.error.
Attempting to write to the lower right corner of a window, subwindow,
or pad will cause an exception to be raised after the character is
printed.
</quote>

Why is this?  What is special about the lower right corner of a
terminal window?  I am guessing this is some relic of the original
terminal era.

TIA!

-- 
boB