hexadecimal.(1) - phpMan

bin_dec_hex (1)      - How to use binary, decimal, and hexadecimal notation.
hexdump (1)          - display file contents in ascii, decimal, hexadecimal, ...
iswxdigit (3)        - test for hexadecimal digit wide character
iswxdigit (3p)       - test for a hexadecimal digit wide-character code
isxdigit (3p)        - test for a hexadecimal digit