(PHP 5 >= 5.3.0)
mb_encoding_aliases — Get aliases of a known encoding type
$encoding
   )
   Returns an array of aliases for a known encoding type.
  
encodingThe encoding type being checked, for aliases.
   Returns a numerically indexed array of encoding aliases on success,
    or FALSE on failure
  
   Emits an E_WARNING level error if
   encoding is unknown.
  
Example #1 mb_encoding_aliases() example
<?php
$encoding        = 'ASCII';
$known_encodings = mb_list_encodings();
if (in_array($encoding, $known_encodings)) {
    $aliases = mb_encoding_aliases($encoding);
    print_r($aliases);
} else {
    echo "Unknown ($encoding) encoding.\n";
}
?>
The above example will output something similar to:
Array
(
    [0] => ANSI_X3.4-1968
    [1] => iso-ir-6
    [2] => ANSI_X3.4-1986
    [3] => ISO_646.irv:1991
    [4] => US-ASCII
    [5] => ISO646-US
    [6] => us
    [7] => IBM367
    [8] => cp367
    [9] => csASCII
)