问为什么PHP忽略任何字符串开头的换行符

EN

JSON:
{
    "text": "\n\n\n\n\n\nHere you can find activities to practise your reading skills. Reading will help you to improve your understanding of the language and build your vocabulary.\n\nThe self-study lessons in this section are written and organised according to the levels of the Common European Framework of Reference for languages (CEFR).\n\nThere are different types of texts and interactive exercises that practise the reading skills you need to do well in your studies, to get ahead at work and to communicate in English in your free time."
}

Array
(
    [0] => Array
        (
            [0] =>  
        )
    [1] => Array
        (
            [0] =>  
        )
    [2] => Array
        (
            [0] =>  
        )
    [3] => Array
        (
            [0] =>  
        )
    [4] => Array
        (
            [0] =>  
        )
    [5] => Array
        (
            [0] =>  
        )
    [6] => Array
        (
            [0] => Here you can find activities to practise your reading skills. Reading will help you to improve your understanding of the language and build your vocabulary.
        )

    [7] => Array
        (
            [0] =>  
        )

    [8] => Array
        (
            [0] => The self-study lessons in this section are written and organised according to the levels of the Common European Framework of Reference for languages (CEFR).
        )

    [9] => Array
        (
            [0] =>  
        )

    [10] => Array
        (
            [0] => There are different types of texts and interactive exercises that practise the reading skills you need to do well in your studies, to get ahead at work and to communicate in English in your free time.
        )

)

Array
(
    [0] => Array
        (
            [0] => Here you can find activities to practise your reading skills. Reading will help you to improve your understanding of the language and build your vocabulary.
        )

    [1] => Array
        (
            [0] =>  
        )

    [2] => Array
        (
            [0] => The self-study lessons in this section are written and organised according to the levels of the Common European Framework of Reference for languages (CEFR).
        )

    [3] => Array
        (
            [0] =>  
        )

    [4] => Array
        (
            [0] => There are different types of texts and interactive exercises that practise the reading skills you need to do well in your studies, to get ahead at work and to communicate in English in your free time.
        )

)

        $stop = false;
        $offset = 0;
        while( !$stop ) {
            $stop = (mb_substr($requestText, $offset, 1)!="\n");
            $offset++;
        }
print_r($offset);exit();

class MyController extends BaseController
{
    public function index(Request $request) {

        $input = $request->all();
        if(!isset($input) || empty($input)) {
            return $this->returnJsonResponse($this->badRequestErrorStatus, "Bad Request: Please check the API documentation for its parameters.");
        }

        if(!isset($input["text"]) || empty($input["text"])) {
            return $this->returnJsonResponse($this->badRequestErrorStatus, "Bad Requess: Please provide the text parameter.");
        }

        \Log::info("### New Request Measurements [Chunk Base: " .env("AI_MICROSERVICES_SPELLCHECKER_MAX_REQUEST_TEXT_CHARACTERS_LENGTH"). " Char] ###");

        //--- Capture The Following Block Process Time
        $startMilliseconds = microtime(true)*1000;
        $data['text'] = $this->_chunkText($input["text"]);
        $endMilliseconds = microtime(true)*1000;
        \Log::info(" Chunking Process Time: (( " . ($endMilliseconds - $startMilliseconds) . " )) Milliseconds");
        //---
}

    /**
     * Chunk the passed text according to Business rules.
     *
     * @param String $requestText
     *
     * @return array
     */
    private function _chunkText($requestText) {
        \Log::info("Chunking Process Starts:");

        $stop = false;
        $offset = 0;

        while( !$stop ) {
            $stop = (mb_substr($requestText, $offset, 1)!="\n");
            $offset++;
        }
//        print_r($offset);exit();
}