Hagen - Pragma ADE

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Features
of all, all we get to see is a Lua table, and in ConT E Xt even that one gets sanitized and
optimized into a more useable table. However, as the data that comes with a font is a
good indication of what a font is capable of, we will discuss some of it in an appendix.
In this section we will discuss the basic principles and categories of features.
5.2.2 Feature sets
Because in the next examples we will demonstrate features, we need to know how we
can tell ConT E Xt what features to use. Although you can add explicit feature definitions
to a font specification, I strongly advice you not to do this but use the more abstract
mechanism of feature sets. These are defined as follows:
\definefontfeature
[MyFeatureSet]
[alpha=yes,
beta=no,
gamma=123]
Such a set is bound to a font with the * specifier, as in:
\definefont
[MyFontInstance]
[MyNiceFont*MyFeatureSet at 12pt]
In most cases the already defined default feature set will suffice. It often makes sense
to use that one as base for new definitions:
\definefontfeature
[MyFeatureSet]
[default]
[alpha=yes,
beta=no,
gamma=123]
The second argument can be a list, as in:
\definefontfeature
[MyFeatureSet]
[MyFirstSet,MySecondSet]
[alpha=yes,
beta=no,
gamma=123]
Of course you need to know what features a font support, and one way to find out is:
mtxrun --script font --list --info --pattern=pagella