Some comments in response to Marco's comments (note that I make
various observations that support both sides of this debate):
MC>But there are cases when having or not a ligature affects
the meaning of the text. These are certainly rare and marginal
cases (in fact, this is being discussed after Unicode's 10th
birthday) but they exist and, because the *meaning* of the text
is affected, not only its presentation, the issue should be
addressed at the plain text level.
Some comments have been made that italics is used semantically,
but clearly should not be expressed in plain text. We should
note, though, that the type of meaning borne by such uses of
italics is in the realm of linguistic pragmatics (if your
familiar with that branch of linguistic study), and not
*lexical* semantics. In the case of "wachstube", however, the
semantic distinction borne by the Fraktur ligation is lexical.
In my mind, that a necessary condition for requiring this
meaning to be expressed in plain text. (This condition alone is
not sufficient, however; it must also be at least true that the
ligation is non-predictable and obligatory.)
MC>The contexts where these graphic variations become
significant are mainly historical and meta-linguistic, but they
are nevertheless important for someone.
"Important for someone" is not a sufficient requirement for
something to be expressed in plain text. To a typographer, the
choice of font is important; to a handwriting expert, the
particular shape a person uses for "s" is important; etc. But
such information doesn't belong in plain text.
MC>Do you remember Carlos Levoyer, the guy who was dealing with
ancient Spanish texts? I suggested him to drop all the
ligatures in his old books, and expand them to regular modern
spelling in his on-line edition. But if he does not want to do
so, he may need a way to specify ligatures like "ct" (plus some
special letters, like the long "s"). And, perhaps, he has to do
this in HTML, or in a database field: that is, in plain text,
sort of.
Surely his ligatures are not indicating lexical semantic
distinctions but rather were merely the choice of the
author/typesetter of the document and were non-obligatory in
the Spanish writing system of that time. He may well want to
accurately record and present the ligatures, but the onus for
this case shouldn't be placed on what can be expressed in plain
text.
MC>A non-historical example for the need to control ligatures
in plain text has already been done: the "fi" ligature in
Turkish. In most roman fonts, the dot over "i" disappears in
the "fi" ligature, because it merges with the "f"'s top. This
aesthetic adjustment is perfectly innocent in most languages,
because the dot on "i" has no special meaning (it is just an
heritage from hand writing). In Turkish, however, dotless "i"
is a separate letter so, in certain fonts, the ligature looses
the distinction between "fi" and "fI".
I've suggested in an earlier message in this thread that
ideally all runs of text should be tagged to indicate their
language. If this is done, then it would be possible for that
information to be used by the rendering engine in shaping the
text and for the font developer to specify that the "fi"
ligature *not* be formed for Turkish but that it be formed for
other languages. (Current score, as I recall: OpenType already
provides support for such language-specific substitution; such
support in not currently available in AAT but is being
considered.)
Peter
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