token = _
  / keyword
  / identifier
  / constant
  / string-literal
  / punctuator

preprocessing-token = _
  / header-name
  / identifier
  / pp-number
  / character-constant
  / string-literal
  / punctuator
  / <each non-white-space character that cannot be one of the above>

keyword = _
  / 'auto'
  / '∗'
  / 'if'
  / 'unsigned'
  / 'break'
  / 'inline'
  / 'void'
  / 'case'
  / 'int'
  / 'volatile'
  / 'char'
  / 'long'
  / 'while'
  / 'const'
  / 'register'
  / '_Alignas'
  / 'continue'
  / 'restrict'
  / '_Alignof'
  / 'default'
  / 'return'
  / '_Atomic'
  / 'do'
  / 'short'
  / '_Bool'
  / 'double'
  / 'signed'
  / '_Complex'
  / 'else'
  / 'sizeof'
  / '_Generic'
  / 'enum'
  / 'static'
  / '_Imaginary'
  / 'extern'
  / 'struct'
  / '_Noreturn'
  / 'float'
  / 'switch'
  / '_Static_assert'
  / 'for'
  / 'typedef'
  / '_Thread_local'
  / 'goto'
  / 'union'

identifier = _
  / identifier-nondigit
  / identifier identifier-nondigit
  / identifier digit

identifier-nondigit = _
  / nondigit
  / universal-character-name
  / <other implementation-defined characters>

nondigit = _
  / '_'
  / 'a'
  / 'b'
  / 'c'
  / 'd'
  / 'e'
  / 'f'
  / 'g'
  / 'h'
  / 'i'
  / 'j'
  / 'k'
  / 'l'
  / 'm'
  / 'n'
  / 'o'
  / 'p'
  / 'q'
  / 'r'
  / 's'
  / 't'
  / 'u'
  / 'v'
  / 'w'
  / 'x'
  / 'y'
  / 'z'
  / 'A'
  / 'B'
  / 'C'
  / 'D'
  / 'E'
  / 'F'
  / 'G'
  / 'H'
  / 'I'
  / 'J'
  / 'K'
  / 'L'
  / 'M'
  / 'N'
  / 'O'
  / 'P'
  / 'Q'
  / 'R'
  / 'S'
  / 'T'
  / 'U'
  / 'V'
  / 'W'
  / 'X'
  / 'Y'
  / 'Z'

digit = _
  / '0'
  / '1'
  / '2'
  / '3'
  / '4'
  / '5'
  / '6'
  / '7'
  / '8'
  / '9'

universal-character-name = _
  / '\u' hex-quad
  / '\U' hex-quad hex-quad

hex-quad = _
  / hexadecimal-digit hexadecimal-digit
  / hexadecimal-digit hexadecimal-digit

constant = _
  / integer-constant
  / floating-constant
  / enumeration-constant
  / character-constant

integer-constant =
  / decimal-constant integer-suffix?
  / octal-constant integer-suffix?
  / hexadecimal-constant integer-suffix?

decimal-constant = _
  / nonzero-digit
  / decimal-constant digit

octal-constant = _
  / '0'
  / octal-constant octal-digit

hexadecimal-constant = _
  / hexadecimal-prefix hexadecimal-digit
  / hexadecimal-constant hexadecimal-digit

hexadecimal-prefix = _
  / '0x'
  / '0X'

nonzero-digit = _
  / '1'
  / '2'
  / '3'
  / '4'
  / '5'
  / '6'
  / '7'
  / '8'
  / '9'

octal-digit = _
  / '0'
  / '1'
  / '2'
  / '3'
  / '4'
  / '5'
  / '6'
  / '7'

hexadecimal-digit = _
  / '0'
  / '1'
  / '2'
  / '3'
  / '4'
  / '5'
  / '6'
  / '7'
  / '8'
  / '9'
  / 'a'
  / 'b'
  / 'c'
  / 'd'
  / 'e'
  / 'f'
  / 'A'
  / 'B'
  / 'C'
  / 'D'
  / 'E'
  / 'F'

integer-suffix = _
  / unsigned-suffix long-suffix?
  / unsigned-suffix long-long-suffix
  / long-suffix unsigned-suffix?
  / long-long-suffix unsigned-suffix?

unsigned-suffix = _
  / 'u'
  / 'U'

long-suffix =
  / 'l'
  / 'L'

long-long-suffix = _
  / 'll'
  / 'LL'

floating-constant = _
  / decimal-floating-constant
  / hexadecimal-floating-constant

decimal-floating-constant = _
  / fractional-constant exponent-part? floating-suffix?
  / digit-sequence exponent-part floating-suffix?

hexadecimal-floating-constant = _
  / hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-part floating-suffix?
  / hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-suffix?

fractional-constant = _
  / digit-sequence? '.' digit-sequence
  / digit-sequence '.'

exponent-part = _
  / 'e' sign? digit-sequence
  / 'E' sign? digit-sequence

sign = _
  / '+'
  / '-'

digit-sequence = _
  / digit
  / digit-sequence digit

hexadecimal-fractional-constant = _
  / hexadecimal-digit-sequence? '.' hexadecimal-digit-sequence
  / hexadecimal-digit-sequence '.'

binary-exponent-part = _
  / 'p' sign? digit-sequence
  / 'P' sign? digit-sequence

hexadecimal-digit-sequence = _
  / hexadecimal-digit
  / hexadecimal-digit-sequence hexadecimal-digit

floating-suffix = _
  / 'f'
  / 'l'
  / 'F'
  / 'L'

enumeration-constant =
  identifier

character-constant = _
  / q<'> c-char-sequence q<'>
  / q<L'> c-char-sequence q<'>
  / q<u'> c-char-sequence q<'>
  / q<U'> c-char-sequence q<'>

c-char-sequence = _
  / c-char
  / c-char-sequence c-char

c-char = _
  / <any member of the source character set except
    the single-quote ', backslash \, or new-line
    character>
  / escape-sequence

escape-sequence = _
  / simple-escape-sequence
  / octal-escape-sequence
  / hexadecimal-escape-sequence
  / universal-character-name

simple-escape-sequence = _
  / q<\'>
  / q<\">
  / q<\?>
  / q<\\>
  / q<\a>
  / q<\b>
  / q<\f>
  / q<\n>
  / q<\r>
  / q<\t>
  / q<\v>

octal-escape-sequence = _
  / '\' octal-digit
  / '\' octal-digit octal-digit
  / '\' octal-digit octal-digit octal-digit

hexadecimal-escape-sequence = _
  / '\x' hexadecimal-digit
  / hexadecimal-escape-sequence hexadecimal-digit

string-literal =
  encoding-prefix? '"' s-char-sequence? '"'

encoding-prefix = _
  / 'u8'
  / 'u'
  / 'U'
  / 'L'

s-char-sequence = _
  / s-char
  / s-char-sequence s-char

s-char = _
  / <any member of the source character set except
    the double-quote ", backslash \, or new-line character>
  / escape-sequence

punctuator = _
  / '['
  / ']'
  / '('
  / ')'
  / '{'
  / '}'
  / '.'
  / '->'
  / '++'
  / '--'
  / '&'
  / '*'
  / '+'
  / '-'
  / '~'
  / '!'
  / '/'
  / '%'
  / '<<'
  / '>>'
  / '<'
  / '>'
  / '<='
  / '>='
  / '=='
  / '!='
  / '^'
  / '|'
  / '&&'
  / '||'
  / '?'
  / ':'
  / ';'
  / '...'
  / '='
  / '*='
  / '/='
  / '%='
  / '+='
  / '-='
  / '<<='
  / '>>='
  / '&='
  / '^='
  / '|='
  / ','
  / '#'
  / '##'
  / '<:'
  / ':>'
  / '<%'
  / '%>'
  / '%:'
  / '%:%:'

header-name = _
  / '<' h-char-sequence '>'
  / '"' q-char-sequence '"'

h-char-sequence = _
  / h-char
  / h-char-sequence h-char

h-char =
  <any member of the source character set except
    the new-line character and \>>

q-char-sequence = _
  / q-char
  / q-char-sequence q-char

q-char = _
  <any member of the source character set except
    the new-line character and ">

pp-number = _
  / digit
  / '.' digit
  / pp-number digit
  / pp-number identifier-nondigit
  / pp-number 'e' sign
  / pp-number 'E' sign
  / pp-number 'p' sign
  / pp-number 'P' sign
  / pp-number '.'