Contextual Substitutions help

Hi, im trying to set up a substitution for f’ in the context of fi

I coded it as: sub f’ i by f.alt;
I also tried: sub i f’ by f.alt;

Neither yielded any substitutions.
What am I doing wrong?

The first line is what you want.
Where did you put that? And how did you test this?

I put the code in as a new feature.
Tested after hitting “compile” and typing in a new text window within glyphs

That feature name has to be “liga” or any of the other liga features (dlig or rlig). You need to stick to a defined feature name otherwise the apps don’t know what to do with it.

Sorry to be a pain, im still new to this.
Ive been using feature type “calt”. Is this not correct?

In fact, I cannot get any substitution features to work. Im missing something here. Im using Glyphs 3.0
I followed instructions from this blog post…

As @GeorgSeifert wrote…

But what type of feature?
Why do they use “calt” in the tutorial?

f_i is a ligature so appears in the liga feature; tutorial here:

Edit, Never mind, I’ve got it worked out now. Thanks for your help!!!

I would put it in the calt feature. There’s also a contextual alternates tutorial.