This is ingenious!

If anybody is curious at to how this works, they use a feature in OpenType (the most common format for modern fonts and the basis for WOFF and EOT) called glyph substitution. It's designed to combine adjacent characters for ligatures and the like. It lets you specify that some arrangement of characters should be replaced by an alternate glyph.

A more interesting usage of this feature is Hasklig: https://github.com/i-tu/Hasklig/

A monospaced fontface for Haskell, where the operators are presented as ligatures. If only it also included operators from other languages.