A PHP string is a series of characters. PHP uses UTF-8 encoding by default, which means it can handle multi-byte characters like those found in many non-Latin alphabets. Unlike some other languages, PHP doesn't have a separate 'character' type - a single character is simply a string of length 1.

```php
<?php

// $s is a string assigned a literal value
// representing the word "hello" in the Thai language.
// PHP string literals are UTF-8 encoded by default.
$s = "สวัสดี";

// strlen() returns the number of bytes in the string
echo "Len: " . strlen($s) . "\n";

// This loop generates the hex values of all
// the bytes that constitute the string $s.
for ($i = 0; $i < strlen($s); $i++) {
    printf("%x ", ord($s[$i]));
}
echo "\n";

// To count how many characters are in a string, we can use
// the mb_strlen() function from the mbstring extension.
// This correctly handles multi-byte characters.
echo "Character count: " . mb_strlen($s, 'UTF-8') . "\n";

// We can use mb_str_split() to split the string into an array of characters,
// and then iterate over them.
foreach (mb_str_split($s) as $idx => $char) {
    printf("U+%X '%s' starts at %d\n", mb_ord($char), $char, mb_strlen(mb_substr($s, 0, $idx), 'UTF-8'));
}

echo "\nUsing mb_strlen and mb_substr\n";
$i = 0;
while ($i < mb_strlen($s, 'UTF-8')) {
    $char = mb_substr($s, $i, 1, 'UTF-8');
    printf("U+%X '%s' starts at %d\n", mb_ord($char), $char, $i);
    examineChar($char);
    $i++;
}

function examineChar($c) {
    // We can compare a character directly to a string literal
    if ($c === 't') {
        echo "found tee\n";
    } elseif ($c === 'ส') {
        echo "found so sua\n";
    }
}