5 Lexical conventions [lex]

5.9 Alternative tokens [lex.digraph]

1
#
Alternative token representations are provided for some operators and punctuators.¹⁰
2
#
In all respects of the language, each alternative token behaves the same, respectively, as its primary token, except for its spelling.
[Note 1: 
The “stringized” values ([cpp.stringize]) of [ and <: are different, maintaining the source spelling.
— end note]
The set of alternative tokens is defined in Table Clause 3.
Table 3 — Alternative tokens [tab:lex.digraph]
🔗
Alternative
Primary
Alternative
Primary
Alternative
Primary
🔗
<%
{
and
&&
and_eq
&=
🔗
%>
}
bitor
|
or_eq
|=
🔗
<:
[
or
||
xor_eq
^=
🔗
:>
]
xor
^
not
!
🔗
%:
#
compl
~
not_eq
!=
🔗
%:%:
##
bitand
&
10)10)
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”.