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Mailing list for the LaTeX3 project <[log in to unmask]>
Frank Mittelbach <[log in to unmask]>
Wed, 3 Mar 1999 23:15:57 +0100
Mailing list for the LaTeX3 project <[log in to unmask]>
text/plain (97 lines)
the sketch below was written on New Years Eve or somewhere about that time,
triggered by the interesting and good work by Lars on extending the NFSS2 idea
of a font encoding --- i don't know if that work is available yet, if not i
hope he will provide it some time soon at least through interested parties.

(that is i think some of his ideas are wrong or say could be better
represented differently but that is natural if you come up with new ideas,

there have been earlier ideas on these issues but i can't find them right now
and anyway, i think this stuff below (which is hopefully not too terse (being
the result of several evening/night discussions) should give some food for
thought (and perhaps better ideas)

stuff like this (or Lars work) is thinking about new concepts (which might
result in eventually in something like NFSS3 if tried and played with) it is
not really about extending NFSS2 at all even if prototype implementations
would work this way.



Glyph Collections and Font Encodings

\copyright\ 1999 Frank Mittelbach  Chris Rowley

A glyph collection is a collection of glyphs.

In \LaTeX{}, the useful glyph collections, which thus get \LaTeX{}
names, are ones such that every glyph in the collection can be
represented by using a single 8-bit (virtual) font and preferably by a
font that is typically widely available in a large range of
typographic forms.

In \LaTeX{}, \emph{representing a glyph} means that any \LaTeX{}
internal token sequence that is advertised as producing that glyph
will do so (reasonably well).  A font represents a glyph collection if
it represents every glyph in the collection.

In \LaTeX{}, \emph{reasonably well} should mean, for letters and
standard punctuation only, that the expected kerning is produced.

How a particular font represents a \LaTeX{} internal token sequence
is defined as and by the \LaTeX{} \emph{encoding} of that font.

There may therefore be more than one encoding used by fonts that
represent the same glyph collection (some of which may do a better job
than others); but a glyph collection will usually have a major
encoding associated with it.

For example (approx), there is a glyph collection that is everything
that can be represented in a T1 font except thorn, eth and dotlessj:
call this EL (Euro-Latin).  This glyph collection can also be defined
as `a subset of what one expects to be able to produce with a random
PS standard font'.  It is (we think) represented by all fonts that
really do have the following font encodings: LY1, T1 and OT1 (suitably
precisely defined).

This is therefore an excellent candidate as a \LaTeX{} glyph collection.

[??? Glyph collections and/or encodings may need to state which glyphs are

Typesetting text with glyph collections.


When typesetting a document, the font status of the \LaTeX{} document
now has an extra attribute: \emph{current glyph collection}.  This
must be explicitly changed, \ie the system will never change it
internally (except maybe for a single glyph).

The encoding status is now determined by the other aspects of the
current font status (except size??).  The .fd files are now labeled
by glyph-collection and family and specify for each shape/series which
encoding to use and also (as now) which actual \TeX{} font to load and

There are two types of glyphs (\ie of \LaTeX{} internals):

letters and punctuation;

text symbols.

Typesetting the former never (we hope:-) changes the font.

Typesetting the latter may do so (for this symbol only), by either:

changing the glyph collection and hence the font (via the .fd file

explicitly choosing a particular font.