Am 09.09.2025 um 09:59 schrieb Hans Hagen via ntg-context:
On 9/9/2025 9:34 AM, Max Chernoff via ntg-context wrote:
Hi Hans,
OpenType contextual alternates ("calt") seem to be disabled by default
in ConTeXt. However, the OpenType spec recommends that this is enabled
by default
https://learn.microsoft.com/en-us/typography/opentype/spec/
features_ae#tag-calt
and it's enabled by default in both HTML and HarfBuzz
https://drafts.csswg.org/css-fonts/#default-features
https://harfbuzz.github.io/shaping-opentype-features.html
Changing this default in ConTeXt probably isn't possible due to
backwards compatibility concerns, so this is more of an FYI than a
request for any changes to be made.
Background: this came up in a recent TeX.SE question
https://tex.stackexchange.com/a/750767
where a new user was surprised by ConTeXt's default setting since it
makes some fonts render differently than other programs.
We started with opentype support (2005) when there wasn't much info
about it. The reference implementation was uniscribe so we had to guess
and compare with that. The xetex engine was using some libraries and
changed them later on. So we couldn't check that out either.
Now, when it comes to features, those experiences, also with specific
fonts, made us decide for the defaults. Over time the specification
became better and more complete but as you say: we want to remain
compatibility. (I assume that ltx folk spend substantial time on
checking changes in hb every time there is an update in tex live, which
is quite often if i look at git syncing.)
An omission in otf is that the font doesn't specify what features are to
be on by default. Combine that with font usage where users have no
control over features, and we see why soem are just turned on. Probably
the same for some (fixing) heuristics. It's now how tex works: there we
*ask* for something, not being *enforced* to.
If I could motivate myself we could of course make such a list of
default features per font.
Of course one can wonder why we have rlig/lig/clig as well as kern/dist
split into several features when they are supposed to be always on. But
I will not waste time on pondering that.
A simple change is to a additional feature set with all the new
recommended settings. Changes to the list can happen unlike the default
feature set and users can apply it to their own font settings.
\definefontfeature
[standard] % harfbuzz?
[always]
[itlc=yes,
rlig=yes,
liga=yes,
clig=yes,
calt=yes]
\starttext
{\definedfont[name:playwritegbjregular*default]Whereas recognition of
the inherent dignity}
{\definedfont[name:playwritegbjregular*standard]Whereas recognition of
the inherent dignity}
\stoptext
Wolfgang
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