5 Lexical conventions [lex]

5.5 Alternative tokens [lex.digraph]

Alternative token representations are provided for some operators and punctuators.17
In all respects of the language, each alternative token behaves the same, respectively, as its primary token, except for its spelling.18
The set of alternative tokens is defined in Table 1.
Table 1 — Alternative tokens
Alternative
Primary
Alternative
Primary
Alternative
Primary
<%
{
and
&&
and_­eq
&=
%>
}
bitor
|
or_­eq
|=
<:
[
or
||
xor_­eq
^=
:>
]
xor
^
not
!
%:
#
compl
~
not_­eq
!=
%:%:
##
bitand
&
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 of [ and <: will be different, maintaining the source spelling, but the tokens can otherwise be freely interchanged.