OpenType fonts deploy powerful typographic features that you may not know about.
Here’s an excerpt from a helpful article on the ILoveTypography.com website:
“The Type1 format where 256 characters are assigned to keys on our keyboard, is becoming a thing of the past. We now design and produce OpenType fonts which can consist of thousands of characters — additional ligatures, various figure sets, small caps, stylistic alternates, … — referred to as glyphs. With these many sets of glyphs integrated in a single font, we are faced with the challenge of including definitions instructing the applications we’re using when to show which glyph. Simply adding a glyph with a ligature to your font doesn’t mean the application you’re using knows when or how to apply it. Whether you want your typeface to change the sequence of f|f|i into the appropriate ligature or want to use old-style figures instead of tabular, you’ll need to add features to your font — glyph substitution definitions — to make it happen.
In this article we’ll give you a look behind the scenes of OpenType substitution features — a general rather than comprehensive overview as the subject is simply too vast. We’ll start casually and work our way to more complex features and ideas. All examples that we will discuss should be considered starting points, just to pique your interest. Read on and find out that it’s really not difficult!”