The use of an undefined escape sequence leads to undefined behavior.
Escape sequences supported in every C and C++ standard are: \n, \t, \v, \b, \r,
\f, \a, \\, \?, \', \", \<Octal Number>, and
\x<Hexadecimal Number>.
C99 and C++11 introduced escape sequences for Unicode characters in the form: \u<4 Hexadecimal Digits> and \U<8
Hexidecimal Digits>.
C++23 supports named escape sequences for Unicode characters in the form \N{<Name of Character>} and a delimited version of
escape sequences is supported: \o{<Octal Number>}, \x{<Hexadecimal Number>}, and \u{<Hexadecimal
Number>}.
Noncompliant code example
const char_t a[ 2 ] = "\k"; // Noncompliant
const char_t b[ 2 ] = "\b"; // Compliant
