To get Unicode numbers out of a UTF-8 string, this can be used, for example:
<?php
print mb_encode_numericentity ('sāш日', array (0x0, 0xffff, 0, 0xffff), 'UTF-8');
?>(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)
mb_encode_numericentity — 文字を HTML 数値エンティティにエンコードする
$string,$map,$encoding = null,$hex = false
   stringの中で指定した文字コードを
   文字コードから HTML 数値エンティティに変換します。
  
変換後の文字列を返します。
   map が整数のリストでない場合、
   ValueError がスローされます。
  
| バージョン | 説明 | 
|---|---|
| 8.4.0 | mapが整数のリストでない場合、
       mb_encode_numericentity() は
       ValueError をスローするようになりました。 | 
| 8.0.0 | encodingは、nullable になりました。 | 
例1 map の例
<?php
$convmap = array (
 int start_code1, int end_code1, int offset1, int mask1,
 int start_code2, int end_code2, int offset2, int mask2,
 ........
 int start_codeN, int end_codeN, int offsetN, int maskN );
// Specify Unicode value for start_codeN and end_codeN
// Add offsetN to value and take bit-wise 'AND' with maskN, then
// it converts value to numeric string reference.
?>
例2 mb_encode_numericentity() の例
<?php
$str = "aAæÆあア𩸽";
/* Convert all UTF8 characters up to 4 bytes to HTML numeric character reference */
$convmap = [0, 0x1FFFFF, 0, 0x10FFFF];
var_dump(mb_encode_numericentity($str, $convmap, "utf8"));
/* Converts only 2-byte and 4-byte UTF8 characters to HTML numeric character reference */
$convmap = [
    0x80, 0x7FF, 0, 0x10FFFF,
    0x10000, 0x1FFFFF, 0, 0x10FFFF,
];
var_dump(mb_encode_numericentity($str, $convmap, "utf8"));
?>上の例の出力は以下となります。
string(46) "aAæÆあア鸽" string(28) "aAæÆあア鸽"
To get Unicode numbers out of a UTF-8 string, this can be used, for example:
<?php
print mb_encode_numericentity ('sāш日', array (0x0, 0xffff, 0, 0xffff), 'UTF-8');
?>Here is a better explanation of convmap:
https://stackoverflow.com/questions/35854535/better-explanation-of-convmap-in-mb-encode-numericentityWe were experiencing difficulties with PHP/Sablotron on Solaris; placing HTML character references into the XSL transformation, when set to output UTF-8, converts them back into UTF8 encoded chars.  This was then a problem for non unicode storage.  Using a bit of code from http://homepage.mac.com/marko/ the following function converts the string back to character references:
function utf2html ($utf2html_string)
{
    $f = 0xffff;
    $convmap = array(
/* <!ENTITY % HTMLlat1 PUBLIC "-//W3C//ENTITIES Latin 1//EN//HTML">
    %HTMLlat1; */
     160,  255, 0, $f,
/* <!ENTITY % HTMLsymbol PUBLIC "-//W3C//ENTITIES Symbols//EN//HTML">
    %HTMLsymbol; */
     402,  402, 0, $f,  913,  929, 0, $f,  931,  937, 0, $f,
     945,  969, 0, $f,  977,  978, 0, $f,  982,  982, 0, $f,
    8226, 8226, 0, $f, 8230, 8230, 0, $f, 8242, 8243, 0, $f,
    8254, 8254, 0, $f, 8260, 8260, 0, $f, 8465, 8465, 0, $f,
    8472, 8472, 0, $f, 8476, 8476, 0, $f, 8482, 8482, 0, $f,
    8501, 8501, 0, $f, 8592, 8596, 0, $f, 8629, 8629, 0, $f,
    8656, 8660, 0, $f, 8704, 8704, 0, $f, 8706, 8707, 0, $f,
    8709, 8709, 0, $f, 8711, 8713, 0, $f, 8715, 8715, 0, $f,
    8719, 8719, 0, $f, 8721, 8722, 0, $f, 8727, 8727, 0, $f,
    8730, 8730, 0, $f, 8733, 8734, 0, $f, 8736, 8736, 0, $f,
    8743, 8747, 0, $f, 8756, 8756, 0, $f, 8764, 8764, 0, $f,
    8773, 8773, 0, $f, 8776, 8776, 0, $f, 8800, 8801, 0, $f,
    8804, 8805, 0, $f, 8834, 8836, 0, $f, 8838, 8839, 0, $f,
    8853, 8853, 0, $f, 8855, 8855, 0, $f, 8869, 8869, 0, $f,
    8901, 8901, 0, $f, 8968, 8971, 0, $f, 9001, 9002, 0, $f,
    9674, 9674, 0, $f, 9824, 9824, 0, $f, 9827, 9827, 0, $f,
    9829, 9830, 0, $f,
/* <!ENTITY % HTMLspecial PUBLIC "-//W3C//ENTITIES Special//EN//HTML">
   %HTMLspecial; */
/* These ones are excluded to enable HTML: 34, 38, 60, 62 */
     338,  339, 0, $f,  352,  353, 0, $f,  376,  376, 0, $f,
     710,  710, 0, $f,  732,  732, 0, $f, 8194, 8195, 0, $f,
    8201, 8201, 0, $f, 8204, 8207, 0, $f, 8211, 8212, 0, $f,
    8216, 8218, 0, $f, 8218, 8218, 0, $f, 8220, 8222, 0, $f,
    8224, 8225, 0, $f, 8240, 8240, 0, $f, 8249, 8250, 0, $f,
    8364, 8364, 0, $f);
    return mb_encode_numericentity($utf2html_string, $convmap, "UTF-8");
}To improve handling of EURO-Symbols in dan at boxuk dot com's function add the following line to $convmap:
128,128,0, $f,