Typographic ligatures are a feature of a font where
multiple characters are combined as one to improve readability. For
example, if you look closely at the
fl in the
following, you'll notice they look slightly different with ligatures
and without ligatures:1
You can in fact create a font that declares any sequence of characters to be a ligature to be rendered differently. Because the difference is only at the font rendering level, copy and paste still work as expected. This allows us to choose sequences of characters that really act like single characters in a given programming language and render them as such.