string mb_convert_case ( string $str , int $mode [, string $encoding = mb_internal_encoding() ] )
//Performs case folding on a string, converted in the way specified by mode.
//对一个 string 进行大小写转换，转换模式由 mode 指定。

<?php
/**
 * Created by PhpStorm.
 * User: zhangrongxiang
 * Date: 2018/1/28
 * Time: 下午3:16
 */

/**Example #1 mb_convert_case() 例子*/
$str = "mary had a Little lamb and she loved it so";
$str = mb_convert_case( $str, MB_CASE_UPPER, "UTF-8" ) . PHP_EOL;
echo $str; // 输出 MARY HAD A LITTLE LAMB AND SHE LOVED IT SO
$str = mb_convert_case( $str, MB_CASE_TITLE, "UTF-8" ) . PHP_EOL;
echo $str; // 输出 Mary Had A Little Lamb And She Loved It So

/**Example #2 非拉丁 UTF-8 文本的mb_convert_case() 例子*/
$str = "Τ?χιστη αλ?πηξ βαφ?? ψημ?νη γη, δρασκελ?ζει υπ?ρ νωθρο? κυν??";
$str = mb_convert_case( $str, MB_CASE_UPPER, "UTF-8" ) . PHP_EOL;
echo $str; // 输出 Τ?ΧΙΣΤΗ ΑΛ?ΠΗΞ ΒΑΦ?Σ ΨΗΜ?ΝΗ ΓΗ, ΔΡΑΣΚΕΛ?ΖΕΙ ΥΠ?Ρ ΝΩΘΡΟ? ΚΥΝ?Σ
$str = mb_convert_case( $str, MB_CASE_TITLE, "UTF-8" ) . PHP_EOL;
echo $str; // 输出 Τ?χιστη Αλ?πηξ Βαφ?σ Ψημ?νη Γη, Δρασκελ?ζει Υπ?ρ Νωθρο? Κυν?σ

/**
 * mb_strtolower() - 使字符串小写
 * mb_strtoupper() - 使字符串大写
 * strtolower() - 将字符串转化为小写
 * strtoupper() - 将字符串转化为大写
 * ucfirst() - 将字符串的首字母转换为大写
 * ucwords() - 将字符串中每个单词的首字母转换为大写
 */

echo mb_convert_case( 'AAA "aaa"', MB_CASE_TITLE ) . PHP_EOL; //Aaa "aaa"
// but  I want this ===> AAA "Aaa"

function mb_convert_case_utf8_variation( $s ) {
    $arr    = preg_split( "//u", $s, - 1, PREG_SPLIT_NO_EMPTY );
    var_dump($arr);
    $result = "";
    $mode   = false;
    foreach ( $arr as $char ) {
        $res = preg_match(
                   '/\\p{Mn}|\\p{Me}|\\p{Cf}|\\p{Lm}|\\p{Sk}|\\p{Lu}|\\p{Ll}|' .
                   '\\p{Lt}|\\p{Sk}|\\p{Cs}/u', $char ) == 1;
        if ( $mode ) {
            if ( ! $res ) {
                $mode = false;
            }
        } elseif ( $res ) {
            $mode = true;
            $char = mb_convert_case( $char, MB_CASE_TITLE, "UTF-8" );
        }
        $result .= $char;
    }
    
    return $result;
}

echo mb_convert_case_utf8_variation('AAA "aaa"').PHP_EOL;
//AAA "Aaa"

echo mb_convert_case("Hello 中国",MB_CASE_UPPER).PHP_EOL;//HELLO 中国
echo mb_convert_case("Hello 中国",MB_CASE_UPPER,"GBK").PHP_EOL;//HELLO 中国