PHP 26 English letter increments ____php

/**
 * Capital Letter Increment
 * * 
 chr () function returns the character from the specified ASCII value
 * ORD () function returns the ASCII value of the first character of the string
 * * 
 @param string $str A -Z English Letter
 * @return String */
function azincrement ($str)
{
    //parameter is converted to uppercase
    $STR = Strtoupper ($str );
    Returns the ASCII value of the parameter
    $str = Ord ($str);
    
    if ($str < | | | $str >) {
        //parameter does not conform to expected return
        ' What kind of ghost are you passing over? ';
    }
    
    if ($str = =) {
        //parameter is the lowest English letter Z, can not increment return
        ' is already z. ';
    }
    
    Return Chr ($STR + 1);
}

Echo azincrement (3);
echo ' <br/> ';
echo azincrement (' Z ');
echo ' <br/> ';
echo azincrement (' B ');
echo ' <br/> ';
echo azincrement (' H ');

Output the following:

What kind of ghost are you passing over?
It's already Z, it's not going to increase.
C
I