Over at I Love Typography, Nick Shinn’s posted a refreshingly clear introduction to OpenType typography’s most essential building block, the alternate character. It’s probably been covered several times before on other sites, but I like how Nick’s simplified his explanation. This is a piece explaining what’s so interesting about OpenType at its most basic levels–and then goes on to show several examples, concepts to make it work, and historically relevant dates. If you’re a beginning-level typographer, there’s also a bit of scripting thrown in there that will prove valuable to your own work and learning.
Typography’s the field that seems closest to pure programming these days, and as such, the communication from that discipline can be opaque for practitioners from the more intuitive areas of design. Nice to have the veil pulled away every once in a while.