what does truncate-partial-width-windows mean?

[Xah Lee]

There's this variable truncate-partial-width-windows in emacs 23.1.

I think it's documentation is not very clear. I read the doc
carefully, together with associated var such as word-wrap and truncate-
lines. However, i cannot find out what exactly this variable do or its
effects, after spending about 30 min setting various combination of
values to these variables and or adjusting my frame width.

following is particular detail on why i didn't find it clear.
--------------------------------
The doc reads this:

> Non-nil means truncate lines in windows with less than the frame width.

this seems to be that this var only has effect when its val is less
than frame width. So i set it to 30.

> For an integer value, truncate lines in each window with less than the
> full frame width, provided the window width is less than that integer;
> otherwise, respect the value of `truncate-lines'.

I don't see any effect. It is not clear to me what this clause means:
“truncate lines in each window with less than the full frame width”.
It's not clear pratically, and it's ambiguous. Does the “with less
than” being a codition where this takes effect, or does it mean it is
the effect of this var? Also, the emacs tradition of using “truncate
lines” can probably be improved. Usually, i understand it to mean “let
long lines run off the right frame width”. It does not actually
_truncate_ lines. In most of today's editors, similar feature is
usually called “no word wrap” or “no line wrap”. This seems much more
clear to me. So, in conjunction with this report on doc issue of
truncate-partial-width-windows, perhaps emacs doc would consider
change the wording of “truncate” in related documentation about line
wrapping.

In any case, i cannot understand what this paragraph means.

> For any other non-nil value, truncate lines in all windows with
> less than the full frame width.

> A value of nil means to respect the value of `truncate-lines'.

> If `word-wrap' is enabled, you might want to reduce this.

In short, i tried to set this to 30 or 150. 30 is less than my frame
width, and 150 is more. And tried to turn on off or set to other value
the other mentioned vars, but i can't see the effect.

Thanks.

  Xah
∑ http://xahlee.org/

☄