подстрока — PHP: str_replace не работает (другие ответы по SO не помогли)

Я написал следующий SSCCE, чтобы продемонстрировать, что у меня есть string (некоторого HTML), и я использую simple_html_dom парсер, чтобы узнать div с определенным значением class приписывать. Это отлично работает. Но мне нужно это убрать div из родительской строки. Так что я использую str_replace, но это не похоже на работу. Пожалуйста, скажите мне, почему и каково решение.

Я проверил решения вопросов, касающихся аналогичных проблем, но они не применились или не помогли решить мою проблему. Я также пытался использовать str_replace_first от этот вопросответ Bas. Но это тоже не работает.

Вы можете увидеть на скриншоте, что он просто печатает весь $haystack после печати --------,

$haystack = '<div class="region-content"  style="margin-right:100px; margin-left:100px;">
<div role="main"><span id="maincontent"></span><div class="que description informationitem notyetanswered" id="q6"><h4 class="accesshide">Question text</h4><input type="hidden" name="q3:6_:sequencecheck" value="1" /><div class="qtext"><p style="font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; margin: 0px 0px 20px; padding: 0px; color: #464646; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: #ffffff;">Schools expect textbooks to be a valuable source of information for students. My research suggests, however, that textbooks that address the place of Native Americans within the history of the United States distort history to suit a particular cultural value system. In some textbooks, for example, settlers are pictured as more humane, complex, skillful, and wise than Native Americans. In essence, textbooks stereotype and depreciate the numerous Native American cultures while reinforcing the attitude that the European conquest of the New World denotes the superiority of European cultures. Although textbooks evaluate Native American architecture, political systems, and homemaking, I contend that they do it from an ethnocentric, European perspective without recognizing that other perspectives are possible. </p>
<p style="font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; margin: 0px 0px 20px; padding: 0px; color: #464646; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: #ffffff;">One argument against my contention asserts that, by nature, textbooks are culturally biased and that I am simply underestimating children\'s ability to see through these biases. Some researchers even claim that by the time students are in high school, they know they cannot take textbooks literally. Yet substantial evidence exists to the contrary. Two researchers, for example, have conducted studies that suggest that children\'s attitudes about particular cultures are strongly influenced by the textbooks used in schools. Given this, an ongoing, careful review of how school textbooks depict Native Americans is certainly warranted.</p></div><div class="im-controls"><input type="hidden" name="q3:6_-seen" value="1" /></div></div>

<div class="que multichoice deferredfeedback notyetanswered" id="q7"><div class="qtext"><p><span style="color: #464646; font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none; background-color: #ffffff;">Which of the following would most logically be the topic of the paragraph immediately following the passage?</span></p></div><div class="ablock"><div class="prompt">Select one:</div><div class="answer"><div class="r0"><input type="radio" name="q3:7_answer" value="0" id="q3:7_answer0" /><label for="q3:7_answer0">a. <span style="color: #464646; font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none; background-color: #ffffff;">the contributions of European immigrants to the development of the United States</span></label> </div>
<div class="r1"><input type="radio" name="q3:7_answer" value="1" id="q3:7_answer1" /><label for="q3:7_answer1">b. <span style="color: #464646; font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none; background-color: #ffffff;"><span class="Apple-converted-space"> </span>the centrality of the teacher\'s role in United States history courses</span></label> </div>
<div class="r0"><input type="radio" name="q3:7_answer" value="2" id="q3:7_answer2" /><label for="q3:7_answer2">c. <span style="color: #464646; font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none; background-color: #ffffff;">nontraditional methods of teaching United States history</span></label> </div>
<div class="r1"><input type="radio" name="q3:7_answer" value="3" id="q3:7_answer3" /><label for="q3:7_answer3">d. <span style="color: #464646; font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none; background-color: #ffffff;">specific ways to evaluate the biases of United States history textbooks <br /></span></label> </div>
<div class="r0"><input type="radio" name="q3:7_answer" value="4" id="q3:7_answer4" /><label for="q3:7_answer4">e. <span style="color: #464646; font-family: HelveticaNeueW01-55Roma, Helvetica, Arial, san-serif; font-size: 14.4444446563721px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: 19.5px; orphans: auto; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none; background-color: #ffffff;">ways in which parents influence children\'s political attitudes <br /></span></label> </div>
</div></div></div>';

require('C:/xampp/htdocs/simple_html_dom.php');
$html = str_get_html($haystack);
foreach($html->find('div[class=que description informationitem notyetanswered]') as $h) {
$reading_passage_outertext = $h->outertext;
}
$hay = str_replace($reading_passage_outertext, "", $haystack);
echo $reading_passage_outertext;
echo '---------------------------------------------------------------------------------------------------------------';
echo $hay;