From: Asmus Freytag (email@example.com)
Date: Sat Apr 18 2009 - 21:54:20 CDT
On 4/18/2009 4:59 PM, Andrew West wrote:
> 2009/4/18 Asmus Freytag <firstname.lastname@example.org>:
>> And, in this case all of you are wrong ;-)
>> The way these fonts work, and the way the SYMBOL charset is designed, was to
>> allow BOTH the use of ASCII and the PUA.
>> To see this, try (on Windows):
>> Run Wordpad
>> Select Wingdings
>> Type F04A
>> Press Alt+X
>> -> you will see the smiley
>> Now type J
>> -> you will see another smiley
>> In other words, both 004A and F04A end up displaying the same glyph.
> And, in this case you are wrong as well ;-)
> There is no mapping of the glyph to 004A in the font's CMAP table.
You will note that I've been very careful not to claim anything about
the CMAP table :)
> fact that the smiley glyph is displayed for "J" is a Windows thing,
> whereby it adds an extra mapping layer from F020..F0FF in the font to
> ASCII codepoints if the font has a symbol encoding.
> This is no doubt
> for compatibility with pre-Unicode symbol fonts that did use ASCII
> mappings, but nevertheless the font itself does not have these ASCII
> mappings, only the Unicode ones.
Which is what I wrote (to restore the quote):
> The way the designers of this feature explained this to me (a long
> time ago) it allowed fonts to support the PUA so that they would not
> overload the ASCII codes, but at the same time, existing fonts that
> were mapped to the ASCII range would continue to function, as would
> existing (pre-Unicode) applications that expected symbol fonts to be
> mapped to the ASCII area.
What the font does in this instance is almost totally irrelevant to
either users and applications, because most applications don't access
fonts directly, they access the various levels of text services provided
by the OS (i.e. Windows, in this case).
Therefore, for all practical purposes, the text can be encoded either as
ASCII or in the PUA.
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