ctype_xdigit
    (PHP 4 >= 4.0.4, PHP 5)
ctype_xdigit -- 
     Check for character(s) representing a hexadecimal digit
    
Description
bool 
ctype_xdigit ( string text)
     Returns TRUE if every character in text is 
     a hexadecimal 'digit', that is a decimal digit or a character from 
     [A-Fa-f] , FALSE otherwise.
    
     
Example 1. A ctype_xdigit() example 
<?php $strings = array('AB10BC99', 'AR1012', 'ab12bc99'); foreach ($strings as $testcase) {     if (ctype_xdigit($testcase)) {         echo "The string $testcase consists of all hexadecimal digits.\n";     } else {         echo "The string $testcase does not consist of all hexadecimal digits.\n";     } } ?>
 |  
 
       This example will output :
       The string AB10BC99 consists of all hexadecimal digits.
The string AR1012 does not consist of all hexadecimal digits.
The string ab12bc99 consists of all hexadecimal digits.  |  
  | 
    
     See also ctype_digit().