In order to get ligature information for some pair of characters in a font, use the following function.
Return ligature for CHARACTER1 and CHARACTER2, or nil
.
Both characters must belong to the same font.
Unless there’s no such ligature, the value returned by this function is
an instance of a class called ligature
. In the context of this
library, the term “ligature” denotes an instance of this class.
A ligature contains four bits of information accessible as described below.