These include “digraphs” and additional reserved words.
The term
“digraph” (token consisting of two characters) is not perfectly
descriptive, since one of the alternative preprocessing-tokens is
%:%: and of course several primary tokens contain two
characters.
Nonetheless, those alternative tokens that aren't lexical
keywords are colloquially known as “digraphs”.
Thus the “stringized” values ([cpp.stringize]) of
[ and <: will be different, maintaining the source
spelling, but the tokens can otherwise be freely interchanged.