I learned that Prince uses ligatures by default. But how do I turn this off? I saw that

font-variant: prince-opentype();

prevents ligatures in the output, but is that syntactically correct?

Does that actually work? I would have thought it doesn't, as you are not specifying any OpenType features to apply.

Hmm, you're right, that doesn't work, I must have checked the wrong output, sorry. But the question is still how to to turn this off. I could do something like this.

font-variant: prince-opentype(xyz);
or
font-variant: prince-opentype(noliga);

That works (and Prince log any errors) but it is certainly not the "correct" way?

Yes, either of those will work. Currently there is no official way to turn off ligatures; if you try to apply an empty set of OpenType substitutions, then Prince will apply the default set, including liga.

Ok. I think I'll use noliga, this expresses the intent in an understandable way.
Thanks!

The Prince latest build now supports the font-variant-ligatures property, which can be used to disable ligatures like this:

font-variant-ligatures: none

It is overridden by the font-variant property, which is now a shorthand property, so you will need to apply it with care if you also use small-caps (also available via the new font-variant-caps property).