From: William Overington (WOverington@ngo.globalnet.co.uk)
Date: Wed Mar 12 2003 - 08:20:27 EST
John Hudson wrote as follows.
If you don't intend to use the PUA codepoint in text, there really is no
point in having it at all.
Well, one useful scenario is as follows. Suppose please that one wishes to
process incoming regular Unicode text, using a eutocode typography file to
influence the process, details of the format on the
http://www.users.globalnet.co.uk/~ngo/ast03300.htm web page, and then use
the output Unicode format text stream as codes to look up glyphs in an
ordinary TrueType font, so as to produce a display which includes using some
ligature glyphs. Having a code such as U+E70B for fj and codes for other
characters as part of a consistent set which is published has the advantage
that if various software authors use the eutocode typography file format,
and various people spend time encoding specific eutocode typography files,
(such as for 18th Century English printing with long s ligatures, German
Fraktur printing and the ligatures of languages of the Indian subcontinent),
and various people produce ordinary TrueType fonts with ligature glyphs
encoded using consistent lists of published Private Use Area code points for
ligatures, then the existence of the list of Private Use Area code points
may well help in interoperability, so that, for example, having looked at
the result using a font produced by one artist one may have a look at the
result using a font produced by another artist without needing to change
the contents of the particular eutocode typography file being used for the
processing and having then to reprocess the original text using that second
eutocode typography file.
Another use is that preparing some text using WordPad and other programs,
not for interchange but just for, say, producing a local print of a poster,
having a consistent, widely used set of Private Use Area code points for
ligatures would mean that a poster designer could try out a number of fonts
from various artists without needing to reset the text each time using
whatever code points each font designer used for each particular ligature
I would mention that my thinking on using Private Use Area codes for
ligatures has gradually moved towards the use of the eutocode typography
file rather than interchanging files using Private Use Area code points for
ligatures, yet I do feel that, for local use such Private Use Area
allocations for ligatures as the golden ligatures collection provides are
potentially useful as they do provide for interoperability of fonts which
contain ligatures which fonts are produced by a variety of artists. Use of
the golden ligatures collection is entirely optional, yet it can be used to
try to achieve some level of interoperability of fonts. Indeed, font
designers who produce fonts using advanced font technologies, where the
conversion tables are internal to the font rather than external as with the
eutocode typography file, where the glyphs for ligatures are not accessed
directly may, if they choose, make use of the code point allocations of the
golden ligatures collection so as to allow the glyphs also to be accessed
from other platforms with a hope of some level of interoperability.
Certainly, using the code points of the golden ligatures collection is not
using regular Unicode code point allocations, yet as a self-help facility
amongst end users so that use of fonts containing ligatures is easier, the
golden ligatures collection is perhaps of some practical use.
I accept that the use of Private Use Area encodings does not guarantee
compatibility, yet one can take care to try to make the use of Private Use
Area codes for ligatures and other characters as graceful as possible.
For example, although there is absolutely no requirement at all for me to do
so, and no one has asked me to do so, I decided to make sure that no golden
ligatures code point allocations made in the future will clash with the code
points used for Phaistos Disc Script in the ConScript Registry.
I am happy to point out, in addition, that I do quite like the idea of a
link with traditional letterpress printing where each ligature character was
cast as one piece of metal for the whole ligature and one could actually
pick them up and place them in a composing stick, so the golden ligatures
collection is about art and nostalgia as well as about technology and
practicality of achieving a stylish display using computing equipment.
I have added a new code recently, which is U+E700 STAFF which is a vertical
line from the very top of the glyph and going as far below the 0 line as one
chooses for a particular font. With Quest text I encoded this character
early with a line going vertically from -768 font units to 2048 font units.
This forces the overall display height of the font before I added either of
lowercase y and g, which in fact go down to -512 font units in Quest text,
so the U+E700 character within the font helps in the display process even
though the character is not usually displayed, though it can be displayed
for test purposes if desired.
12 March 2003
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