Most fonts will require a few basic OpenType features. Customers love them too! If you include any sort of alternate version of a character (glyph) in your font, you must also include an OpenType feature for it. Otherwise, it will be difficult for users to access the glyph.
For instance, if your font includes fi and fl ligatures, a feature must be added to your font. Other very common OpenType features include Discretionary Ligatures, Contextual Alternates, Stylistic Sets, Small Caps, and various features for numeral styles.
If your font contains stylistic alternates, please consider making them accessible both via the <SALT> (Stylistic Alternates) feature AND via Stylistic Set(s).
- An Introduction to OpenType Substitution Features
- The OpenType Cookbook
- Glyphs App offers various tutorials related to OpenType features including ligatures or fractions.
- Typofonderie - OpenType Features
- Microsoft Typography - Registered OpenType Features